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Molecular dissection of inborn errors of immunity can help to elucidate the nonredundant functions of individual genes. We studied 3 children with an immune dysregulation syndrome of susceptibility to infection, lymphadenopathy, hepatosplenomegaly, developmental delay, autoimmunity, and lymphoma of B-cell (n = 2) or T-cell (n = 1) origin. All 3 showed early autologous T-cell reconstitution following allogeneic hematopoietic stem cell transplantation. By whole-exome sequencing, we identified rare homozygous germline missense or nonsense variants in a known epigenetic regulator of gene expression: ten-eleven translocation methylcytosine dioxygenase 2 (TET2). Mutated TET2 protein was absent or enzymatically defective for 5-hydroxymethylating activity, resulting in whole-blood DNA hypermethylation. Circulating T cells showed an abnormal immunophenotype including expanded double-negative, but depleted follicular helper, T-cell compartments and impaired Fas-dependent apoptosis in 2 of 3 patients. Moreover, TET2-deficient B cells showed defective class-switch recombination. The hematopoietic potential of patient-derived induced pluripotent stem cells was skewed toward the myeloid lineage. These are the first reported cases of autosomal-recessive germline TET2 deficiency in humans, causing clinically significant immunodeficiency and an autoimmune lymphoproliferative syndrome with marked predisposition to lymphoma. This disease phenotype demonstrates the broad role of TET2 within the human immune system.

CRAC channel regulator 2 A (CRACR2A) is a large Rab GTPase that is expressed abundantly in T cells and acts as a signal transmitter between T cell receptor stimulation and activation of the Ca2+-NFAT and JNK-AP1 pathways. CRACR2A has been linked to human diseases in numerous genome-wide association studies, however, to date no patient with damaging variants in CRACR2A has been identified. In this study, we describe a patient harboring biallelic variants in CRACR2A [paternal allele c.834 gaG> gaT (p.E278D) and maternal alelle c.430 Aga > Gga (p.R144G) c.898 Gag> Tag (p.E300*)], the gene encoding CRACR2A. The 33-year-old patient of East-Asian origin exhibited late onset combined immunodeficiency characterised by recurrent chest infections, panhypogammaglobulinemia and CD4+ T cell lymphopenia. In vitro exposure of patient B cells to a T-dependent stimulus resulted in normal generation of antibody-secreting cells, however the patient’s T cells showed pronounced reduction in CRACR2A protein levels and reduced proximal TCR signaling, including dampened SOCE and reduced JNK phosphorylation, that contributed to a defect in proliferation and cytokine production. Expression of individual allelic mutants in CRACR2A-deleted T cells showed that the CRACR2AE278D mutant did not affect JNK phosphorylation, but impaired SOCE which resulted in reduced cytokine production. The truncated double mutant CRACR2AR144G/E300* showed a pronounced defect in JNK phosphorylation as well as SOCE and strong impairment in cytokine production. Thus, we have identified variants in CRACR2A that led to late-stage combined immunodeficiency characterized by loss of function in T cells.

TTC7A deficiency typically causes severe gastrointestinal manifestations such as multiple intestinal atresia or early-onset inflammatory bowel disease. In some cases, this is associated with severe combined immunodeficiency. Partial loss-of-function mutations appear to be associated with a milder phenotype resulting in common variable immunodeficiency-like condition with enteropathy.

Loss of function or null mutations of Stromal interaction molecule 1 (STIM1) are known to cause early-onset combined immunodeficiency (CID) disease with recurrent and chronic infections, autoimmunity, haemolytic anaemia, ectodermal dysplasia, muscular weakness and myalgia. here we report of novel STIM1 deficiency and 6 year follow up of two previous cases associated with mild immunological phenotype

While widespread genome sequencing ushers in a new era of preventive medicine, the tools for predictive genomics are still lacking. Time and resource limitations mean that human diseases remain uncharacterized because of an inability to predict clinically relevant genetic variants. A strategy of targeting highly conserved protein regions is used commonly in functional studies. However, this benefit is lost for rare diseases where the attributable genes are mostly conserved. An immunological disorder exemplifying this challenge occurs through damaging mutations in RAG1 and RAG2 which presents at an early age with a distinct phenotype of life-threatening immunodeficiency or autoimmunity. Many tools exist for variant pathogenicity prediction, but these cannot account for the probability of variant occurrence. Here, we present a method that predicts the likelihood of mutation for every amino acid residue in the RAG1 and RAG2 proteins. Population genetics data from approximately 146,000 individuals was used for rare variant analysis. Forty-four known pathogenic variants reported in patients and recombination activity measurements from 110 RAG1/2 mutants were used to validate calculated scores. Probabilities were compared with 98 currently known human cases of disease. A genome sequence dataset of 558 patients who have primary immunodeficiency but that are negative for RAG deficiency were also used as validation controls. We compared the difference between mutation likelihood and pathogenicity prediction. Our method builds a map of most probable mutations allowing pre-emptive functional analysis. This method may be applied to other diseases with hopes of improving preparedness for clinical diagnosis. Electronic supplementary material The online version of this article (10.1007/s10875-019-00670-z) contains supplementary material, which is available to authorized users.

Autozygosity mapping has been a powerful method for the identification of autosomal recessive disease genes. However, the approach is limited by the availability of suitable consanguineous pedigrees. While rare autosomal recessive diseases are overrepresented in consanguineous families, a significant proportion of affected patients nonetheless originate in families where the parents are apparently unrelated. However, due to their relative rarity and the heterogeneity of disease alleles, it has proved difficult to use these patients to identify disease loci. Therefore, we developed "Phaser," a computer application that is able to infer the phase of SNP alleles and so haplotype entire chromosomes in small nuclear families (http://dna.leeds.ac.uk/Phaser). Once the index case's chromosomes have been haplotyped, it is then possible to deduce those of the parents and subsequently identify the parental origin of all the siblings' DNA. By combining information from a small number of nuclear families, it may then be possible to identify linkage to the recessive disease locus, in both in-bred and out-bred families. We have illustrated the program's utility by using it to correctly identify both the cystic fibrosis locus (using two unrelated compound heterozygous CEPH families) and a new gene mutated in early-onset myopathy with respiratory distress and dysphagia locus in a single consanguineous pedigree.

Mutations of the presenilin 1 (PS-1) gene at the Alzheimer's disease (AD) FAD3 locus on chromosome 14q24.3 are responsible for the majority of familial early-onset AD. As genes responsible for familial forms of AD are obvious candidates for further investigation in “sporadic” disease, we performed a molecular analysis of PS-1 transcripts extracted from brain tissues of a series of histologically confirmed cases of “sporadic” AD (n = 10) and also from histologically “normal” (non-Alzheimer) age-matched brain controls (n = 5). No sequence changes in the PS-1 coding sequence were detected after analysis by reverse transcription-PCR. This suggests that the frequency of mutations in the PS-1 (S182) coding region in “sporadic” Alzheimer's disease is very low. However, we demonstrated that the PS-1 gene is highly variably spliced. One splice variant involves the 5′ untranslated region of the PS-1 gene only and hence encodes for normal PS-1. Six further splice variants involve coding regions of the PS-1 gene and result in truncated proteins lacking specific transmembrane domains. Most of these variants do not coincide with recognized sites of introns in the PS-1 gene. One of these variants, resulting in the loss of transmembrane domain TM-VII, was found only in an AD patient.

We report a new homozygous CTG-->CCG (Leu-->Pro) mutation at codon 354 in the factor XIIIA gene of a patient suffering from FXIII deficiency. Leu354 lies in a pocket within the core domain of the FXIIIA molecule, with its side chain pointing into the structure of the barrel 1 domain. Replacement of leucine with a proline residue gives rise to steric hindrance between the proline ring and the surrounding residues, and rearrangement of these residues would be necessary for proline to be accommodated at this position. Using PCR-RFLP, we have demonstrated the absence of this mutation from 220 normal alleles. Together, these data suggest that Leu354Pro is likely to be the disease-causing mutation in this factor XIII deficient family.

Background: Inactivation of wild type P53 by its main cellular inhibitors (MDM2 and MDMX) is a well recognised feature of tumour formation in liposarcomas. MDM2 over-expression has been detected in approximately 80% of liposarcomas but only limited information is available about MDMX over-expression. To date, we are not aware of any study that has described the patterns of MDM2 and MDMX co-expression in liposarcomas. Such information has become more pertinent as various novel MDM2 and/or MDMX single and dual affinity antagonist compounds are emerging as an alternative approach for potential targeted therapeutic strategies. Methods. We analysed a case series of 61 fully characterized liposarcomas of various sub-types by immunohistochemistry, to assess the expression levels of P53, MDM2 and MDMX, simultaneously. P53 sequencing was performed in all cases that expressed P53 protein in 10% or more of cells to rule out mutation-related over-expression. Results: 50 cases over-expressed MDM2 and 42 of these co-expressed MDMX at varying relative levels. The relative expression levels of the two proteins with respect to each other were subtype-dependent. This apparently affected the detected levels of P53 directly in two distinct patterns. Diminished levels of P53 were observed when MDM2 was significantly higher in relation to MDMX, suggesting a dominant role for MDM2 in the degradation of P53. Higher levels of P53 were noted with increasing MDMX levels suggesting an interaction between MDM2 and MDMX that resulted in a reduced efficiency of MDM2 in degrading P53. Of the 26 cases of liposarcoma with elevated P53 expression, 5 were found to have a somatic mutation in the P53 gene. Conclusions: The results suggest that complex dynamic interactions between MDM2 and MDMX proteins may directly affect the cellular levels of P53. This therefore suggests that careful characterization of both these markers will be necessary in tumours when considering in vivo evaluation of novel blocker compounds for MDM proteins, as a therapeutic strategy to restore wild type P53 function.

SummaryInherited factor XIII (FXIII) deficiency is an autosomal recessive disorder which results in a serious bleeding diathesis, problems with wound healing and a very high risk of recurrent miscarriage in deficient females. We have analysed the molecular basis of factor XIII deficiency in two patients and their parents, who originate from the North of Pakistan. Four sequence changes were identified: an AGC→AGG (Ser→Arg) FXIII deficiency-causing mutation in codon 295; G→A at position -246 upstream of exon 1; T→C and C→T at positions -23 and -24, respectively, in intron 9. Using molecular modelling we predict that the Ser295Arg mutation would prevent the FXIIIA molecule from folding correctly and thus result in an unstable FXIIIA mutant polypeptide. The sequence changes −246G→A, −23T→C and −24C→T are normal polymorphisms. RT-PCR analysis demonstrates that the intronic sequence changes do not appear to affect the accuracy of FXIIIA RNA processing.

Factor XIII is a transglutaminase essential for normal hemostasis. We have studied the plasma FXIII levels and FXIII activity in 71 individuals and found these to be normally distributed. FXIII specific activity is also normally distributed. However, we show that FXIII activity is not directly dependent on FXIII levels, and individuals with low FXIII levels may have high FXIII activity and vice versa. We have determined the FXIIIA genotype in these individuals to assess whether the variation observed in FXIII specific activity is dependent on specific polymorphisms in the FXIIIA gene. Our data show that the Leu34 and Leu564 variants give rise to increased FXIII specific activity, while the Phe204 variant results in lower FXIII specific activity. We also report preliminary evidence that the Phe204 polymorphism may be associated with recurrent miscarriage. Overall, we have identified 23 unique FXIIIA genotypes. Certain specific FXIIIA genotypes consistently give rise to high, low, or median FXIII specific activity levels, while others appear to have little or no consistent influence on the FXIII phenotype. These genotype to phenotype relationships are discussed in light of the growing interest in the role of FXIII in clinical problems involving an increased thrombotic tendency.

We have investigated the molecular basis of factor XIII (FXIII) deficiency in a family from the north-west region of the U.K. and identified two sequence changes in the FXIII subunit A (FXIIIA) gene. We report a novel Asn to Lys mutation at codon 541, and a g--a mutation at the intron 5/exon 6 splice junction in the FXIIIA gene. The splicing mutation results in two abnormal FXIIIA transcripts. The Asn541 residue is important for stabilizing an external fold in the FXIIIA barrel 1 domain. The Asn541Lys mutation is expected to result in inappropriate folding and therefore an unstable FXIIIA molecule.

Inherited deficiency of factor XIIIA subunit (FXIIIA) is an autosomal recessive disorder that is characterized by a life-long bleeding tendency and complications in wound healing. Molecular genetic studies have shown the deficiency can be due to small sequence changes within the FXIIIA gene, such as point mutations or microdeletions. On molecular analysis of the FXIIIA gene in an FXIII-deficient patient, of United Kingdom origin, we identified a putative homozygous missense mutation, Arg408Gln. However, the father of this patient is homozygous normal for arginine at codon 408. Having proved paternity in this pedigree by microsatellite analysis, we examined the FXIIIA RNA of the patient by reverse transcriptase-polymerase chain reaction and found the paternal allele to lack exons 4 through 11 inclusive. Hence, a huge deletion extending from intron 3 to intron 11 and the Arg408Gln mutation are jointly responsible for FXIIIA deficiency in this family. This is the first finding of such a large deletion in the FXIIIA gene.

SummaryCoagulation factor XIII, a transglutaminase which stabilises blood clots by covalently cross-linking fibrin, is essential for normal haemostasis. FXIII deficiency results in a life-long bleeding disorder with added complications in wound healing and tissue repair. Sequence changes in the human FXIIIA gene, largely missense mutations, are primarily responsible for inherited FXIII deficiency. We have carried out molecular analysis of the FXIIIA gene in two unrelated FXIII deficient individuals and identified three splice site mutations; a g→a at the exon 6 acceptor splice site, a g→a at the exon 7 donor splice site and a coding sequence T→G at the exon 8 donor splice site. We have also examined the FXIIIA mRNA in these patients and find that each mutation gives rise to multiple transcripts which vary in their relative abundance. The precise molecular mechanisms which result in these variant transcripts, and their relative abundance in our FXIII deficient patients, are discussed.

The advent of the discipline of molecular genetics over the past decade has led to a dramatic growth in our understanding of the genetics of a myriad of diseases. Ophthalmology has benefited greatly from this new technology, with significant advances in our knowledge about conditions as varied as aniridia and retinitis pigmentosa.1 2 Our understanding of the genetics of primary open angle glaucoma (POAG) may not be as clear as with some other ophthalmic conditions but, nevertheless, there have been great advances since the last review about the genetics of glaucoma published in the BJO in 1980.3 At that time, our knowledge was based on a number of conflicting studies attempting to link human polymorphisms, such as the ability to taste phenyl thiocarbamide, with glaucoma.4 Nowadays, the positions of genes responsible for various forms of glaucoma have been localised, not just to individual chromosomes, but to specific small regions on those chromosomes. Recently, for the first time, a gene responsible for a specific form of POAG has been identified. This review aims to highlight and explain the important recent advances in our understanding of the genetics of POAG. Primary open angle glaucoma, for the purpose of this review, refers to those cases of glaucoma in which there is not only no evident antecedent or related ocular disease but also the angle of the anterior chamber remains open at all times.5 The possibility of a genetic predisposition to glaucoma was first realised in 1842 when Benedict reported the occurrence of glaucoma in two sisters.6 Despite the intervening 150 years, our understanding of the genetics of POAG remains unclear. Certainly, most POAG pedigrees do not show a simple Mendelian pattern of inheritance. However, relatives of patients with glaucoma do run an increased risk of developing the condition …

Summary. Factor XIII (FXIII) is a zymogen essential for normal haemostasis. In inherited FXIII deficiency the majority of cases show absence of the FXHIa subunit. Molecular analysis of PCR-amplified FXIIIa subunit exonic regions, and of RT-PCR amplified cDNA from six patients with FXIIIa subunit deficiency, from five unrelated families, has revealed 10 sequence changes: three mutations resulting in abnormal splicing of pre-mRNA, one nonsense mutation, one deletion/insertion change, three point mutations producing Val34Leu, Asn60Lys and Arg408Gln changes, and two silent mutations. In three families the patients are homozygous for a specific deficiency causing mutation, and patients from the remaining two families are compound heterozygotes. Understanding the molecular pathology of the disorder provides insights into the structure-function relationships of the various domains within the FXm protein. From a clinical point of view, it enables direct diagnosis at the DNA level and may aid the development of FXIII analogues to promote wound healing.

The Leu564 Factor XIIIA Variant Results in Significantly Lower Plasma Factor XIII Levels than the Pro564 Variant

To determine the phenotype of an Australian pedigree with the myocilin (MYOC) Gly252Arg mutation, comparing it with other pedigrees carrying the same mutation.All recruited subjects underwent a comprehensive clinical examination, including optic disc assessment, applanation tonometry, and visual field measurement. Mutation analysis was performed through direct sequencing. Haplotype analysis was performed using microsatellite markers around the MYOC gene.Eight Gly252Arg mutation carriers with glaucoma were identified from the same pedigree. Carriers' mean +/- SD age at diagnosis was 46.3 +/- 11.4 years (range, 31-60 years). Highest recorded intraocular pressure ranged from 27 to 42 mm Hg (mean +/- SD, 32.4 +/- 5.6 mm Hg). Cup-disc ratios in the worst eye ranged from 0.6 to 0.9. Six of the 8 individuals had undergone filtration surgery. A common founding haplotype between MY5 and D1S218 was found for Caucasian individuals tested with this mutation. One subject was compound heterozygotic for the MYOC Gly252Arg mutation and a novel MYOC Gly244Val variant.Although a common founder for Gly252Arg across Caucasian subjects was found, the phenotype from this Australian MYOC mutation-carrying pedigree is less severe than previously described. The severity of glaucoma caused by the Gly252Arg mutation may be similar to the Thr377Met MYOC mutation, yet is more severe than the most common Gln368Stop mutation.Since its implication in glaucoma, much work has been performed investigating the clinical features of MYOC-related glaucoma. Given the strong genotype-phenotype correlations with MYOC disease-causing variants, health care professionals armed with such molecular information are able to accurately counsel patients on their likely disease course. Our work suggests that the disease associated with MYOC Gly252Arg is less severe than previously described in other pedigrees with this specific mutation.

We identified five disease-causing mutations in six factor XIII deficient patients from four unrelated families: two novel nonsense mutations (nucleotide 979C--T corresponding to Arg326Stop; and nucleotide 2075G--A corresponding to Trp691 Stop), one novel deletion of a single nucleotide (nucleotide 708G or 709G), one previously reported missense mutation (nucleotide 888C--G corresponding to Ser295Arg), and a previously reported splice site mutation (nucleotide 319G--T at the last position of exon 3). The phenotypic consequences of these mutations are discussed.

Objectives. The objectives of this study were 1) to assess the importance of an early diagnosis for factor XIII (FXIII) deficiency, and 2) to investigate the molecular basis and mechanism(s) of disease in the patients under study. Methods. The case histories of 6 FXIII-deficient patients were examined to assess the influence of early versus delayed diagnosis and replacement therapy. The nucleotide sequence of the FXIIIA gene was determined to identify the underlying mutations responsible for the bleeding diathesis in each patient. Molecular modeling was used to predict the mechanism(s) of disease causation for each mutation. Results. All cases presented with umbilical hemorrhage. Patients 1 to 3 were diagnosed, and their prophylactic therapy was commenced in infancy. Diagnosis in patients 4 to 6 was considerably delayed and, as a result, they continued to suffer from many bleeding symptoms. The FXIIIA gene mutations identified in these patients were as follows: a homozygous GAA→AAA mutation in codon 102 (Glu102Lys) in patient 1 and a homozygous AGC→AGG mutation in codon 295 (Ser295Arg) in patients 2 to 6. These mutations segregate with disease and are absent from the normal population, suggesting that they are likely to be disease-causing sequence changes. Computer modeling indicates that both the Lys102 and Arg295 mutants are unable to fold correctly, and probably result in unstable FXIIIA molecules. Conclusions. We demonstrate the importance of recognizing delayed umbilical hemorrhage as a presenting feature for congenital FXIII deficiency, and the value of early diagnosis and prophylaxis. The bleeding disorder of patient 1 was attributable to a homozygous Glu102Lys mutation in FXIIIA. A homozygous Ser295Arg mutation in FXIIIA was responsible for FXIII deficiency in patients 2 to 6.

AIMS A number of genetic loci have been implicated in the pathogenesis of primary open angle glaucoma (POAG). The aim of this study was to identify the genetic cause of POAG in a large Scottish family and, if possible, offer genetic screening and advice to family members. METHODS Family members were examined to determine their disease status. Base excision sequence scanning was carried out in order to test for the presence of a POAG causing mutation at known genetic loci. Direct DNA sequencing was performed in order to determine the mutation sequence. RESULTS All family members of known affected disease status and two family members of unknown disease status were found to have a mutation in the TIGR gene. The mutation resulted in the substitution of a glycine residue with an arginine residue at codon 252 (Gly252Arg). No other sequence variations were present in any members of the family. CONCLUSION The Gly252Arg mutation in the TIGR gene results in the development of POAG in this family. It was possible to identify younger, currently unaffected, members of the family who carry the mutation and who are therefore at a very high risk of developing POAG themselves. This is the first demonstration that Gly252Arg can be a disease causing mutation rather than a benign polymorphism. The possible pathogenic mechanisms and wider implications of the mutation are considered.

The determination of nucleotide sequence is fundamental to the identification and molecular analysis of genes. Direct sequencing of PCR products is now becoming a commonplace procedure for haplotype analysis, and for defining mutations and polymorphism within genes, particularly for diagnostic purposes. A previously unrecognised phenomenon, primer related variability, observed in sequence data generated using Taq cycle sequencing and T7 Sequenase sequencing, is reported. This suggests that caution is necessary when interpreting DNA sequence data. This is particularly important in situations where treatment may be dependent on the accuracy of the molecular diagnosis.

Whilst the majority of inherited diseases have been found to be caused by single base substitutions, small insertions or deletions (

The PstI polymorphism detected by probe KM19 is a highly informative marker in linkage disequilibrium with the cystic fibrosis locus and has been used extensively for prenatal diagnosis. The currently available primers used for polymerase chain reaction- (PCR-) based analysis of this locus have been shown to produce spurious amplification products. In this report, we describe the sequence of the KM19 locus and the major contaminating PCR product. We have used this information to design a more specific amplification procedure for analysis of the KM19 locus.

We describe the construction of a cosmid cloning vector, pMT555, which allows positive selection for the presence of an inserted DNA fragment. The vector contains sequences which enable its replication and selection in either E. coli or Saccharomyces cerevisiae. We demonstrate that pMT555 may be used for the efficient construction of total genomic banks from small quantities of donor DNA. The positive selection permits the stable maintenance of the cosmid in E. coli and the faithful replication of inserted sequences.

The small ring derivative of Saccharomyces cerevisiae chromosome III, which was formed by a cross-over between HML on the left arm and HMR on the right arm, contains three Ty elements. The class II element Ty 1-17 lies immediately centromere-distal to LEU2 on the left arm while two class I elements are tandemly arranged distal to PGK on the right arm. We have sequenced the regions of chromosome III surrounding Ty 1-17 and have defined a region where a number of transposition events have occurred. This region is flanked by the 5' ends of two tRNA genes, tRNA3Glu on the centromere distal side and tRNA3Leu immediately in front of LEU2. Close to the tRNA3Glu gene there is a region containing degenerate delta sequences organised in opposite orientations. Immediately distal to Ty 1-17 there are two complete solo delta elements, one inserted into the other. The sequence indicates that these two delta sequences were inserted into chromosome II by separate transposition events. A model is presented to explain how this structure arose and the role of solo delta elements in transposon propagation and maintenance is discussed.

While widespread genome sequencing ushers in a new era of preventive medicine, the tools for predictive genomics are still lacking. Time and resource limitations mean that human diseases remain uncharacterised because of an inability to predict clinically relevant genetic variants. A strategy of targeting highly conserved protein regions is used commonly in functional studies. However, this benefit is lost for rare diseases where the attributable genes are mostly conserved. An immunological disorder exemplifying this challenge occurs through damaging mutations in RAG1 and RAG2 which presents at an early age with a distinct phenotype of life-threatening immunodeficiency or autoimmunity. Many tools exist for variant pathogenicity prediction but these cannot account for the probability of variant occurrence. Here, we present a method that predicts the likelihood of mutation for every amino acid residue in the RAG1 and RAG2 proteins. Population genetics data from approximately 146,000 individuals was used for rare variant analysis. Forty-four known pathogenic variants reported in patients and recombination activity measurements from 110 RAG1/2 mutants were used to validate calculated scores. Probabilities were compared with 98 currently known human cases of disease. A genome sequence dataset of 558 patients who have primary immunodeficiency but that are negative for RAG deficiency were also used as validation controls. We compared the difference between mutation likelihood and pathogenicity prediction. Our method builds a map of most probable mutations allowing pre-emptive functional analysis. This method may be applied to other diseases with hopes of improving preparedness for clinical diagnosis.

The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.