Bacteriophage N4-induced transcribing activities in E. coli. III. A third cistron required for N4 RNA polymerase II...

The requirement of a third gene product of molecular weight 15,000 for coliphage N4 middle RNA synthesis is described. Therefore, three proteins of molecular weights 15,000, 30,000, and 40,000, which constitute the N4 RNA polymerase II activity, are required for N4 middle RNA synthesis. A complementation assay for N4 RNA polymerase II activity, which requires a DNA-membrane complex carrying the 15,000-MW protein and a supernatant providing the 30,000- and 40,000-MW proteins, has been developed. This assay, which reproduces the requirement for the cistron 5 gene product in vitro provides a means for the purification of the soluble components of the N4 RNA polymerase II activity (to be reported elsewhere). The cistron 5 gene product is also required for N4 RNA polymerase II to synthesize RNAs utilizing middle promoters resident in recombinant plasmids. Mechanisms by which the cistron 5 gene product affects N4 RNA polymerase II transcription in vivo and in vitro are discussed.