ESCHERICHIA-COLI CIS-ACTING 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 regul ation of the glyA gene. The glyA deletion results in 25% of the normal serine hydroxymethyltransferase activity. Three classes of mutants wi th increased glyA expression were isolated on glycine supplemented pla tes. One class of mutations increased glyA expression 10-fold by direc tly altering the - 35 consensus sequence of the glyA promoter, The two other classes increased glyA expression about 2- and 6-fold, respecti vely. 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 ope ron, encoding the glycine cleavage enzyme system. The mutations were m apped to about minute 85.5 on the E. coli chromosome.