Association of Bacteriophage Lambda N Gene Protein with E. coli RNA Polymerase

Abstract

INTRODUCTION
Gene expression in prokaryotes appears to be regulated primarily at the level of transcription (Chamberlin 1974). In some systems, alterations in transcriptional activity can be correlated with physical changes in the structure of RNA polymerase, such as modifications of the core subunits or association of new polypeptides with the enzyme (Stevens 1972; Greenleaf, Linn and Losick 1973; Horvitz 1973; Goff 1974; Ratner 1974).

We are interested in the molecular details of the regulation of gene expression in bacteriophage λ, a system known to exhibit an intricate pattern of transcriptional control. One essential λ gene required for proper early transcription is the N gene, the product of which appears to be required for the elongation of “immediate-early” transcripts into the adjacent “delayed-early” genes (see Figure 1) (Herskowitz 1973). Although the mechanism of N action remains unclear, several models of N function have been proposed, including suggestions that N protein antagonizes the host transcription termination factor rho (Roberts 1971) and that N protein stabilizes distal messenger from rapid degradation (Brunel and Davison 1975). The isolation of several host mutations that specifically block N function (Georgopoulos 1971; Ghysen and Pironio 1972; Friedman, Jolly and Mural 1973) and the finding that some of these mutations map in the cistron coding for the β subunit of RNA polymerase have led to the suggestion that the N protein interacts with RNA polymerase. Such an interaction has also been postulated by Friedman, Wilgus and Mural (1973) to explain the apparent immunity specificities of N^λ and N²¹,...