Search

The highly conserved Saccharomyces cerevisiae RAD51 protein functions in both mitotic and meiotic homologous recombination and in double-strand break repair. Screening of the public cDNA sequence database for RAD51-like genes led to the identification of a partial sequence from a breast tissue library present in the I.M.A.G.E. (Integrated Molecular Analysis of Genes and their Expression) collection. An extended 1764-bp cDNA clone encoding an open reading frame of 350 amino acids was isolated. This clone showed significant amino acid identity with other human RAD51 homologs. The new homolog, named RAD51B, was mapped to human chromosome 14q23-q24.2 using a panel of human-hamster somatic cell hybrids and fluorescence in situ hybridization. Northern blot analysis demonstrated that RAD51B mRNA is widely expressed and most abundant in tissues active in recombination. Functions associated with known RAD51 homologs suggest a role for RAD51B in meiotic recombination and/or recombinational repair.

We have used exon amplification to identify putative transcribed sequences from an 823-kb contig consisting of 28 cosmids that form a minimum tiling path from the interval 19p12-p13.1. This region contains the genes responsible for multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). We have trapped 66 exons (an average of 2.4 exons per cosmid) from pools of 2 or 3 cosmids. The majority of exons (51.5%) show only weak similarity or no similarity (36.3%) to sequences in current databases. Six of 8 exons examined from these groups, however, show cross-species sequence conservation, indicating that many of them probably represent authentic exons. Eight exons show identity or significant similarity to ESTs or known genes, including the human TNF receptor 3 '-flanking region gene, human epoxide hydrolase (EPHX), human growth/differentiation factor (GOF-1), human myocyte-specific enhancer factor 2, the rat neurocan gene, and the human cartilage oligomeric matrix protein gene (COMP). Mutations in this latter gene have recently been shown to be responsible for MED and PSACH.

In the course of isolation and sequence analysis of microsatellite repeat containing human cDNAs, we have isolated the human homologue of the rat visinin-like peptide gene. The human gene shows a high degree of conservation at both the amino acid and the DNA sequence level. The (CA)n microsatellite repeat embedded in the 3' untranslated region of the gene is conserved between rat and human, along with the flanking DNA sequences. We have mapped the VSNL1 gene to the short arm of chromosome 2.

Using a high-speed flow cytometer/sorter, we constructed spot-blot "stamps" measuring 3.5 x 2.0 cm containing 21 separate human chromosome fractions. Through hybridization to these stamps, 20 randomly selected cDNAs were assigned to specific chromosomes. Sequencing and BLAST database screening confirmed the location of one gene (UCHL1) and allowed the assignment of two other previously identified genes (LRP130 and cDNA IB871.)