Identification and control of synthesis of the dsdC activator protein.

Operon fusions between the D-serine deaminase regulatory and structural genes and lacZ were constructed and used to examine the control of expression of the positive regulatory gene, dsdC. Merodiploid strains containing both dsdCp::Mu d (lac Apr) and dsdC+A+ produced only one-fourth as much beta-galactosidase as did the haploid dsdCp::Mu d (lac Apr) strains, indicating that the dsdC+ product repressed its own synthesis. The repression was reversed by D-serine. dsdC expression was not depressed in a cya background. The basal level of D-serine deaminase was the same in wild-type and dsdCp fusion strains. The dsdC gene product was identified in maxicell strains harboring dsd plasmids as a 34,000-dalton protein. dsdC gene transcription proceeded clockwise; thus, its promoter is adjacent to that of dsdA.