Mutational analysis of a bacteriophage P4 late promoter.

Transcription from the late Psid promoter of satellite bacteriophage P4 is dependent on the bacterial RNA polymerase carrying the sigma 70 subunit and is positively regulated by the product of the P4 delta gene or the ogr gene of helper bacteriophage P2. Through deletion and mutational analyses of the Psid promoter, we identified mutations in the -10 region and in a region of hyphenated dyad symmetry centered around position -55 that inactivate Psid. Most of these mutations alter base pairs that are highly conserved in the five other delta-activated P4 and P2 late promoters. We propose that the P4 delta and P2 ogr gene products bind the -55 region of the P4 and P2 late promoters.