Role of bacteriophage Mu C protein in activation of the mom gene promoter.

The phage Mu C gene product is a specific activator of Mu late gene transcription, including activation of the mom operon. Fusion of the C gene to the efficient translation initiation region of the Escherichia coli atpE gene allowed significant overproduction of C protein, which was subsequently purified and assayed for DNA binding by gel retardation and nuclease footprinting techniques. C protein binds to a site immediately upstream of the -35 region both of the mom promoter and the related phage D108 mod promoter. The location of the mom promoter has been determined by primer extension. Upstream deletions extending more than 3 base pairs into the C-binding site abolished activation of the mom promoter in vivo. In vitro binding of C was not significantly affected by DNA methylation. A second, C-dependent promoter was identified just downstream of the C coding region; comparison with the mom promoter revealed common structural elements.