Orientation of separated DNA strands of coliphage 186 relative to its genetic map

Control of gene expression in the temperate coliphage 186. IX. B is the sole phage function needed to activate transcription of the phage late genes

Using plasmid clones we have determined that the late control function B is the only phage function that is needed to activate a late promoter of coliphage 186, and we predict that it functions as an auxiliary factor to RNA polymerase in the activation of late transcription. We have also shown that a high concentration of B will activate late transcription from a prophage, and we conclude that replicating DNA is not a template requirement for B to function. The original demonstration of a need for the replication gene A in late transcription can be explained by the fact that replication leads to an increase in B gene dosage, with the consequent increase in B concentration leading to the efficient activation of the late promoters.

Control of gene expression in the temperate coliphage 186. VIII. Control of lysis and lysogeny by a transcriptional switch involving face-to-face promoters

The lysogenic and early lytic operons of the temperate coliphage 186 are transcribed divergently. Primer extension mapping of the 5' ends of these in vivo transcripts showed that the rightward lytic promoter, pR, and the leftward lysogenic promoter, pL, are arranged face-to-face, with their transcripts overlapping by 60 bases. We examined the control of transcription from pR and pL using galK as a reporter gene. The product of the lysogenic cI gene strongly repressed pR transcription while allowing pL transcription. The product of the lytic apl gene (formerly CP75) strongly repressed pL transcription while allowing pR transcription. Thus, the cI-pR-pL-apl region functioned as a transcriptional switch, determining whether transcription was lytic or lysogenic. Also, the cI gene product was able to stimulate pL, possibly by alleviating an inhibition of pL transcription caused by convergent transcription from pR. Other consequences of the face-to-face promoter arrangement are discussed.

Control of gene expression in the P2-related template coliphages. III. DNA sequence of the major control region of phage 186

The PstI fragment (65.5% to 77.4%) of coliphage 186, known genetically to encode the major control genes, has been sequenced, and an analysis performed to assess coding capacity, transcription-translation signals, and to identify any other significant features. Our analysis indicates that the region encodes: seven genes, including the int and cI genes, which overlap, the late control gene B, and two genes, named CP75 and CP76, encoding potential DNA-binding proteins; a promoter pB and terminator tB for the rightward transcription of the B gene, and we predict the existence of this transcript in a lysogen; a promoter pL and terminator tL for leftward transcription that encodes the int and cI genes, and represents the presumed lysogenic transcript; a promoter pR for rightward transcription to give the presumed (early) lytic transcript that is overlapping and convergent with the lysogenic transcript; and finally, a potential operator site for repressor binding in the region of the pR promoter. Preliminary evidence is presented to support this analysis.