Mutational analysis of a C-dependent late promoter of bacteriophage Mu.

Late transcription of bacteriophage Mu initiates at four promoters, P(lys), PI, PP and Pmom, and requires the Mu C protein and the host RNA polymerase. Promoter-containing DNA fragments extending approximately 200 bp upstream and downstream of the 5' starts of the lys, I and P transcripts were cloned into a multicopy lacZ-expression plasmid. Promoter activity, assayed by beta-galactosidase expression, was determined under two different conditions: (1) with C provided from a compatible plasmid in the absence of other Mu factors and (2) with C provided from an induced Mu prophage. beta-galactosidase activities were greatest for P(lys), intermediate for PI, and lowest for PP. Similar analysis of plasmids containing nested sets of deletions removing 5' or 3' sequences of P(lys) demonstrated that a 68-bp region was sufficient for full activity. Point mutations were generated within the 68-bp region by mutagenic oligonucleotide-directed PCR (Mod-PCR). Properties of the lys promoter mutants indicated that, in addition to the -10 region, a 19-bp region from -52 to -34 containing the C footprint is required for C-dependent promoter activity.