Direct selection of expressed sequences within a 1-Mb region flanking BRCA1 on human chromosome 17q21.

Direct selection of genes within the interval of chromosome 17q21 containing BRCA1 was performed. YAC and cosmid contigs spanning the BRCA1 region were used to select cDNA clones from pools of cDNAs derived from human placenta, HeLa cells, activated T cells, and fetal head. A minimum set of 48 fragments of nonoverlapping cDNAs that unequivocally mapped within a 1-Mb region was identified, although it is not yet known how many of these are derived from the same transcript. DNA sequence analyses revealed that 4 of these cDNAs were derived from known genes (EDH17B2, glucose-6-phosphatase, IAI.3B, and E1AF), 1 is a member of a previously described gene family (HMG-17), and 7 share substantial identity with previously described genes from human or other species. The remainder showed no significant homology to known genes. Limited PCR-based expression profiles of a set of 13 of the genes were performed, and all gave positive results with at least some cDNA sources supporting the contention that they truly represent transcribed sequences. A comparison between genes obtained from this region by direct selection with those obtained by direct screening or exon trapping (see accompanying papers, this issue) revealed that over 90% of the genes identified by exon trapping were represented in the selected material and that at least two additional genes that appear to represent low abundance transcripts with restricted expression profiles were identified by selection but not by other means.