Search

A receptor for atrial natriuretic peptide (ANP) was purified 2700-fold, to apparent homogeneity, from cultured bovine aortic smooth muscle cells by affinity chromatography. The native ANP receptor has a molecular weight of 125,000 as determined by both metrizamide gradient centrifugation and nonreducing NaDodSO4/polyacrylamide gel electrophoresis. With 125I-labeled ANP as ligand, the purified receptor bound a maximum of 5.70 nmol of ligand per mg of protein and the dissociation constant was 4.0 X 10(-10)M. Upon treatment with 10 mM dithiothreitol, the purified receptor migrated as a single band at Mr 60,500 in NaDodSO4/polyacrylamide gel electrophoresis. These findings show that the holoreceptor for ANP in vascular tissue is composed of two subunits of identical apparent molecular weight, presumably linked by a disulfide bridge(s).

Plant gene products that could play a role in the process of symbiotic nitrogen fixation in leguminous plants were detected by screening a cDNA library prepared from soybean nodule poly(A)(+) RNA. About 13% of the 5,700 clones screened contained sequences detectable with a root cDNA probe while about 2,100 clones (37% of the library) contained sequences that were detectable only with nodule cDNA. Five unique sequence species, accounting for more than half of the 2,100 nodule-specific clones, were identified by cross-hybridization experiments. The most abundant species, represented by 860 clones, encodes the well-characterized protein, leghemoglobin (Lb). The other four species, designated NodA, NodB, NodC, and NodD, are represented by 350, 55, 61, and 6 clones, respectively. Each of these four species was found to be encoded by the plant nuclear genome at low copy number. The transcripts corresponding to the nodule-specific clones represented 12-15% (Lb), 6% (NodA), and 0.5-1.1% (NodB, NodC, and NodD) mole fraction of nodule polysomal mRNAs but could not be detected in root polysomal RNA. Hybrid-selection of nodule mRNAs by representative clones and in vitro translation indicated that polypeptides of M(r) 44,000, 27,000, 24,000, and 100,000-120,000 are encoded by NodA, NodB, NodC, and NodD sequences, respectively. These polypeptides reacted with antiserum prepared against total soluble nodule proteins suggesting that the cloned sequences encode nodule-specific proteins, nodulins.

Recombinant bacterial plasmids have been constructed by inserting double-stranded chicken procollagen cDNA sequences linked to chemically synthesized decanucleotides containing HindIII sites into the HindIII site of pBR322. After transformation of Escherichia coli chi1776, colonies were selected by ampicillin resistance and recombinants containing procollagen sequences were identified by colony hybridization to 32P-labeled procollagen cDNA. The inserts from three recombinant plasmids, pCg10, pCg13, and pCg45, were 1200, 2200, and 2550 base pairs long respectively. Their sequence homology has been established by restriction mapping and crosshybridization of nick-translated plasmids to Southern blots of Hpa II fragments of the inserts, pCg45 has been positively identified as containing the pro alpha2 collagen sequence by partial determination of the DNA sequence of its ends: it has a short thymine-rich sequence at one end and a sequence coding for residues 478--499 in the chicken alpha2 chain at the other end.

A closed duplex DNA molecule relaxed and containing nucleosomes has a different linking number from the same molecule relaxed and without nucleosomes. What does this say about the structure of the nucleosome? A mathematical study of this question is made, representing the DNA molecule by a ribbon. It is shown that the linking number of a closed ribbon can be decomposed into the linking number of a reference ribbon plus a sum of locally determined "linking differences."

The nucleotide sequence of the glycoprotein genes of fully virulent Sindbis virus and derived mutants that have reduced neurovirulence for neonatal mice (attenuated mutants) has been determined. A single amino acid difference, arginine instead of serine at position 114 of the mature E2 glycoprotein, distinguished the prototype attenuated mutant from its virulent wild-type parent. Virulent revertants of the attenuated mutant showed same-site reversion to the wild-type sequence. An identical single amino acid substitution, an arginine for the serine at E2 position 114, was found in a second independently selected attenuated mutant. The strains are characterized by genetic linkage between attenuation, accelerated penetration of baby hamster kidney cells, and efficient neutralization by the E2-specific monoclonal antibodies R6 and R13; selection for change in one property simultaneously selected for change in the other two (Olmsted, R. A., Baric, R. S., Sawyer, B. A. & Johnston, R. E. (1984) Science 225, 424-427 and Olmsted, R. A., Meyer, W. J. & Johnston, R. E. (1986) Virology 148, 1-10). The nucleotide sequence data suggest that a single mutation in the E2 gene is sufficient to cause these coordinate phenotypic changes. These findings identify a single locus in a Sindbis virus surface glycoprotein gene that determines both efficiency of interaction with cultured baby hamster kidney cells and degree of virulence in neonatal mice.

A geometric invariant of a space curve, the writhing number, is defined and studied. For the central curve of a twisted cord the writhing number measures the extent to which coiling of the central curve has relieved local twisting of the cord. This study originated in response to questions that arise in the study of supercoiled double-stranded DNA rings.