The Escherichia coli MutH protein is not the repressor of the bacteriophage Mu mom operon

Abstract

Expression of the bacteriophage Mu mom-operon is under tight regulatory control. One of the factors required for transcription of the operon is the host Escherichia coli Dam activity. It was proposed that DNA methylation by this enzyme prevents the binding of a cellular repressor to an operator site containing three 5'-GATC-3' sequences, the known target site of Dam methylation. Support for this model came from the observation of others that the requirement for Dam was almost completely suppressed in a mutH-lysA deletion mutant, suggesting that the MutH protein is the postulated transcriptional repressor. In this communication, however, I show that the Dam requirement is not effectively relieved in this deletion mutant; therefore, the MutH protein alone is not the mom repressor.