Dominance Studies with Stable Merodiploids in the d -Serine Deaminase System of Escherichia coli K-12

Abstract

An episome, F32, which carries the genetic markers dsdC+, the presumed structural gene for D-serine deaminase, dsdX+, a regulatory locus governing the synthesis of D-serine deaminase, aroC+, and purC+ was obtained from strain AB311 of E. coli K-12, and was used to construct appropriate merodiploids with dsdC markers. In all dsdC/dsdC+ diploids examined, dsdC was found to be cis dominant, trans recessive, to dsdC+. In 2 cases, however, the cis dominance was only partial. Moreover, complementation was observed between one of the dsdC markers which is fully cis dominant and one which is partially cis dominant. Because of the size of the dsdC region, the phenotypes of the mutants, and the partial trans dominance of dsdC+ over some of the dsdC mutations, the dsdC region may specify a product, but that this product does not move with facility through the cytoplasm.