Escherichia coli K-12 and B Contain Functional Bacteriophage P2 ogr Genes

The bacteriophage P2 ogr gene encodes an essential 72-amino-acid protein which acts as a positive regulator of P2 late transcription. A P2 ogr deletion phage, which depends on the supply of Ogr protein in trans for lytic growth on Escherichia coli C, has previously been constructed. E. coli B and K-12 were found to support the growth of the ogr-defective P2 phage because of the presence of functional ogr genes located in cryptic P2-like prophages in these strains. The cryptic ogr genes were cloned and sequenced. Compared with the P2 wild-type ogr gene, the ogr genes in the B and K-12 strains are conserved, containing mostly silent base substitutions. One of the base substitutions in the K-12 ogr gene results in replacement of an alanine with valine at position 57 in the Ogr protein but does not seem to affect the function of Ogr as a transcriptional activator. The cryptic ogr genes are constitutively transcribed, apparently at a higher level than the wild-type ogr gene in a P2 lysogen. Bacteriophage P2 represents a family of noninducible temperate coliphages which differ from the lambdoid phages with respect to both genetic organization and regulation (for a review, see reference 7). The phage P2 ogr gene encodes a 72-amino-acid basic protein (10, 16) that functions as a positive regulator of transcription from the P2 late promoter