[Study of the regulation of crp gene expression in Escherichia coli K12].

The regulation of crp gene expression by CRP-cAMP complex was studied in E. coli strain by the crp-lac operon fusion. F'141 crp+ episome decreased 5-7 fold the high level of crp-lac expression in crp strains while F'141 crp episome had no effect. The hybrid plasmid pCAP2 crp+ with the intact crp gene did not affect the crp gene expression level in crp mutants, though they had acquired the Crp+ phenotype just as they did in F'141 crp+ presence. The F'141 crp+ and pCAP2 crp+ combination in crp mutants also resulted in decrease of the crp gene expression comparable to the registered in the presence of the F'141 crp+ plasmid. Similar repression occurred only in cya+ strains but not in cya strains. The crp gene is supposed to possess negative regulation by CRP-cAMP complex with a complementary factor also necessary. The latter is evidently located in an E. coli chromosome site overlapped by F'141 episome.