Cross-specificities between cII-like proteins and pRE-like promoters of lambdoid bacteriophages.

We have investigated the activation of transcription from the pRE promoters of phages lambda, 21 and P22 by the lambda and 21 cII proteins and the P22 c1 (cII-like) protein, using an in vivo system in which cII protein from a derepressed prophage activates transcription from a pRE DNA fragment on a multicopy plasmid. We find that each protein is highly specific for its own cognate pRE promoter, although measureable cross-reactions are observed. The primary recognition sequence for cII protein on lambda pRE is a pair of TTGC repeat sequences in the sequence 5'-TTGCN6TTGC-3' at the -35 region of the promoter. This same sequence is found in 21 pRE, while P22 pRE has the sequence 5'-TTGCN6TTGT-3', which is the same as that of lambda ctr1, a pRE+ variant of lambda. lambda ctr1 pRE is half as active as lambda + pRE when assayed with either the lambda cII or the P22 c1 proteins. Therefore, the single base change in the P22 repeat sequence cannot explain why the P22 c1 protein is much more active with P22 pRE than lambda pRE. The dya5 mutation, a G----A change at position -43 of pRE, makes pRE a stronger promoter when assayed with either the lambda or 21 cII proteins or the P22 c1 protein. We conclude that efficient activation of a cII-dependent promoter by a cII protein requires sequence information in addition to the TTGC repeat sequences. We do not know the characteristics of the proteins which are responsible for the specificity of each protein for its own cognate promoter.(ABSTRACT TRUNCATED AT 250 WORDS)