In vivo D-serine deaminase transcription start sites in wild-type Escherichia coli and in dsdA promoter mutants.

The D-serine deaminase structural (dsdA) and regulatory (dsdC) genes are transcribed with opposite polarity from an intergenic region comprising more than 600 base pairs. The order of genes in the dsd region is supN-dsdA-dsdC-aroC---his. The DNA sequence of the intergenic region has been slightly revised from a previously published version (E. McFall and L. Runkel, J. Bacteriol. 154:1508-1512, 1983). The dsdA gene is preceded by a long open reading frame. The dsdA in vivo transcription start sites for the wild type (base pair +1) and for three phenotypically distinct promoter constitutive mutants were determined by the S1 nuclease method. They are identical and are located about 81 base pairs upstream of the translation start site. D-Serine deaminase regulation is normal in rho mutants. Possible mechanisms for dsdA activation are discussed.