The Isolation of cDNAs from OATL1 at Xp11.2 Using a 480-kb YAC

Using an ornithine-δ-aminotransferase (OAT) cDNA, we identified five YACs that cover two nonadjacent OAT-related loci in Xp11.2-p11.3, designated OATL1 (distal) and OATL2 (proximal). Because several retinal degenerative disorders map to this region, we used YAC2 (480 kb), which covers the most distal part of OATL1, as a probe to screen a retinal cDNA library. From 8 × 10⁴ plaques screened, we isolated 13 clones. Two were OAT cDNAs. The remaining 11 were divided into eight groups by cross-hybridization. Groups 1-4 contain cDNAs that originate from single-copy X-linked genes in YAC2. Each has an open reading frame of >500 bp and detects one or more transcripts on a Northern blot. The gene for each was sublocalized and ordered in YAC2. The cDNAs in groups 5-8 contained two or more Alu sequences, had no open reading frames, and did not detect transcripts. The cDNAs from groups 1-4 provide expressed sequence tags and identify candidate genes for the genetic disorders that map to this region.