Here we report the isolation, characterization and chromosome localization of a subtracted cDNA (CBS-1) isolated from the human ocular ciliary body which encodes a novel protein. As is deduced from the nucleotide sequence of the cDNA, CBS-1 contains an open reading frame consisting of 182 amino acids, with a molecular weight of 19.5kDa. CBS-1 shares significant nucleotide and amino acid sequence identities (residues 51 to 182) with a hypothetical 15.5kDa protein in the ANSA-GAP intergenic region (yeaA) of Escherichia coli, and the carboxyl terminal region of pilB, a transcription factor involved in the regulation of expression of pili, from Neisseria gonorrhoeae. Interestingly, CBS-1 also shares significant identity with the carboxyl terminus of the peptide-methionine sulfoxide reductase (MsrA), a repair enzyme, from Helicobacter pylori and Streptococcus pneumoniae. However, the amino terminal of CBS-1 (residues 23 to 43), which lacks homology to the amino terminal region of gonococcal pilB or pneumococcal MsrA, exhibits significant identity in a stretch of 20 amino acids, with glycine-rich proteins. By Northern blot, CBS-1, hybridized to a 0.6 to 0.7kb transcript in size, is expressed ubiquitously in many tissues, but most abundantly in the retina and ocular ciliary body, skeletal muscle and heart. An epitope-directed antibody to an amino acid sequence at the carboxyl terminus of CBS-1 recognized a main protein of 19.5kDa in ocular ciliary body extracts, and a 23kDa protein in total extracts from E. coli MC1061 cells, which expresses high levels of MsrA. The CBS-1 gene was mapped to human chromosome 10p12 between markers WI-8535 and WI-4724, and is tightly linked to the two STRP markers of D10S1789 and D10S550. We suggest that the CBS-1 gene encodes a mammalian transcription factor related to the bacterial pilB and certain bacterial MsrA homologues.