AUTOGENOUS REGULATION OF THE ECORII METHYLASE GENE AT THE TRANSCRIPTIONAL LEVEL - EFFECT OF 5-AZACYTIDINE

mRNA of the EcoRII methylase (M.EcoRII), a type II modification enzyme , was induced when Escherichia coli carrying a cloned M.EcoRII gene wa s exposed to the bacteriocidal drug 5-azacytidine. Induction occurred only when transcription was initiated from its own promoter. When the 5' promoter sequences were deleted or replaced with the lac promoter s equences, no induction occurred. The induction was independent of the template DNA level, but the presence of an intact M.EcoRII protein was a requirement. The drug is incorporated into DNA which then inhibits M.EcoRII by binding tightly to the enzyme. A deletion within the M.Eco RII coding region caused a marked increase in the basal level of mRNA transcribed from the M.EcoRII promoter, but no induction occurred upon 5-azacytidine treatment. The level could be reduced to normal by M.Ec oRII in trans. In vitro, the enzyme bound to the sequences upstream of the transcription start sites and inhibited the initiation of transcr iption. These experiments indicate that expression of the M.EcoRII gen e was autogenously regulated at the transcriptional level. Similar reg ulation is also noted in another DNA (cytosine-5) methylase, M.MspI.