Regulation of diaminopimelate decarboxylase synthesis in Escherichia coli. I. Identification of a lysR gene encoding an activator of the lysA gene.

The synthesis of diaminopimelate decarboxylase, which catalyzes the decarboxylation of diaminopimelate into lysine, is known to be repressed by lysine and induced by diaminopimelate in Escherichia coli K12. Until now only mutations in lysA, the structural gene for diaminopimelate decarboxylase, have been described that lead to a Lys- phenotype. A set of plasmids carrying adjacent inserts of the lysA region was constructed and employed to transform different Lys- mutants. The complementation pattern observed and the corresponding expression of the lysA gene show that in fact the Lys- phenotype can be obtained by mutations in two different and closely linked loci: one being the lysA structural gene, and the other called lysR. We propose that the lysR gene encodes a positive effector required for the full expression of the lysA gene. The synthesis of a hybrid lysA-lacZ protein constructed in vitro was observed to be decreased dramatically in lysR mutants. Moreover, all the regulatory features were lost, indicating that the LysR activator is necessary for the regulation of lysA expression. The gene order is thyA lysA lysR clockwise around 61 minutes on the chromosome, lysA being transcribed counter-clockwise.