Differential effect of phage regulator functions on transcription from various promoters: evidence that the P22 gene 24 and the lambda gene N products distinguish three classes of promoters.

Abstract

Early rightward transcription of the λ genome which normally initiates from P r can also initiate from two promoters (c17 and ric5b) generated by mutations. In the absence of the phage-specified N regulatory function, transcription initiating from either of these promoters cannot proceed through the P-Q region due to a transcription termination sequence, t r 2. We have used expression of the R gene product, endolysin, as an indirect measure of transcription of genes lying distal to t r 2. Our studies indicate that whereas transcription initiating from P r can utilize N product in overcoming transcription termination, transcription initiating either at c17 or ric5b cannot similarly utilize N product. Using hybrid phage constructed from λ and a Salmonella-specific temperate phage P22, we find that a P22 gene product can be utilized by transcription initiating both at P r and ric5b (but not transcription initiating at c17) in overcoming termination. Our studies indicate that the P22 gene 24 product is the function involved, a P22 function previously shown to have properties similar to those of the N function of λ (Hilliker, 1974) . These observations permit the identification of three types of promoters found on various λ derivatives; (1) P r which can utilize the N and 24 gene products (2) ric5b which can utilize only the gene 24 product, and (3) c17 which can utilize neither product.