Regulation in Escherichia coli of the porin protein gene encoded by lambdoid bacteriophages.

Specialized lambda transducing phages carrying the cloned lc porin gene from the lambdoid bacteriophage PA-2, including various amounts of a sequence 5' to the start of transcription, were used to study the regulation of the porin gene. It was found that a cyclic AMP receptor protein consensus binding site 65 base pairs 5' to the start of transcription was required for catabolite repression of lc but was not sufficient for maximum expression under derepressing conditions. A sequence located more than 209 base pairs 5' to the start of transcription was necessary for maximum expression. By manipulating the copy number of the lc gene and the temperature and by measuring both the rate of synthesis of mRNA and the amount of Lc protein in the outer membrane, it was determined that the expression of lc is regulated primarily at the level of transcription and that expression is not autoregulated. Evidence is also presented that the silent phage porin gene nmpC of Escherichia coli K-12 is transcribed to the same extent as lc even though it does not give rise to a stable pool of mRNA. The structure of the 5' end of lc and nmpC is similar to that of ompF, and a model for transcriptional regulation is presented which may apply to all of these porin genes.