Effect of ptsI and ptsH mutations on initiation of transcription of the Escherichia coli lactose operon.

Mutations in the pts genes (which code for the enzyme I and HPr protein - the general components of the phosphoenolypyruvate-dependent phosphotransferase system) lead to decreases in enzyme-inducible synthesis at the level of transcription. The intracellular content of cyclic AMP in the ptsIH mutant was severely diminished, while the ptsH bacteria contain the same amounts of this nucleotide as the wild-type cells. Nevertheless expression of the lac operon was diminished in the ptsH as well as in the ptsIH mutant. The exogenous cyclic AMP did not prevent repression of beta-galactosidase synthesis in a delta cya ptsI mutant in a wide range of concentrations in the growth medium (from 0.05 mM to 5 mM). The combination of ptsI or ptsH mutations with rpoC1 (synthesis of thermosensitive beta' subunit of RNA polymerase) leads to greater disturbance of beta-galactosidase production at the nonpermissive temperature than demonstrated in the pts+ rpoC1 strain. The stimulatory effect of exogenous cyclic AMP was more pronounced in pts rpoC1 than in pts+ rpoC1 bacteria. The data presented confirm the hypothesis that pts mutations alter the function of CRP in initiation of transcription.