Escherichia coli cis- and trans-acting mutations that increase glyA gene expression

We used an Escherichia coli strain blocked in serine biosynthesis and carrying a partial glyA deletion to isolate strains with altered regulation of the glyA gene. The glyA deletion results in 25% of the normal serine hydroxymethyltransferase activity. Three classes of mutants with increased glyA expression were isolated on glycine supplemented plates. One class of mutations increased glyA expression 10-fold by directly altering the -35 consensus sequence of the glyA promoter. The two other classes increased glyA expression about 2- and 6-fold, respectively. The latter two classes of mutations also affected regulation of the metE gene of the folate branch of the methionine pathway, but not metA in the nonfolate branch of the methionine pathway, or the gcv operon, encoding the glycine cleavage enzyme system. The mutations were mapped to about minute 85.5 on the E. coli chromosome.