Physical mapping of the Escherichia coli D-serine deaminase region: contiguity of the dsd structural and regulatory genes.

The genes dsdA, dsdO, and dsdC have been located on a 3.0-kilobase pair (kb) fragment of the Escherichia coli chromosome by a combination of techniques. The loci were first cloned onto lambda and various plasmid vectors. dsd hybrid plasmids were then digested with restriction enzymes, and the fragments were recloned to test for the presence of dsdC or dsdA. In one case, a 4.2-kb restriction fragment containing the dsdA operon was used to form a heteroduplex with a well-defined lambda dsd deoxyribonucleic acid. The results show that dsdA, dsdO, and at least 0.6 kb of dsdC are present on this piece of deoxyribonucleic acid. On the basis of the mapping analysis and the molecular weight of D-serine deaminase, 1.9 kb of the 4.2-kb fragment is accounted for by the three dsd loci. We conclude that dsdO and dsdC are contiguous. A detailed dsd restriction map is presented.