THE BLOOMS-SYNDROME GENE-PRODUCT IS HOMOLOGOUS TO RECQ HELICASES

The Bloom's syndrome (BS) gene, BLM, plays an important role in the ma intenance of genomic stability in somatic cells. A candidate for BLM w as identified by direct selection of a cDNA derived from a 250 kb segm ent of the genome to which BLM had been assigned by somatic crossover point mapping. In this novel mapping method, cells were used from pers ons with BS that had undergone intragenic recombination within BLM. cD NA analysis of the candidate gene identified a 4437 bp cDNA that encod es a 1417 amino acid peptide with homology to the RecQ helicases, a su bfamily of DExH box-containing DNA and RNA helicases. The presence of chain-terminating mutations in the candidate gene in persons with BS p roved that it was BLM.