In vitro transcription of the early region of Caulobacter phage .vphi.Cd1 deoxyribonucleic acid by host RNA polymerase

Publisher Website
Google Scholar
Abstract
Transcription of the C. crescentus phage .vphi.Cd1 genome requires both the host RNA polymerase and a phage-encoded, rifampicin-resistant RNA polymerase. Transcription of the early region of the .vphi.Cd1 genome was examined in vitro with C. crescentus RNA polymerase. Four transcripts, A, B, C and D, which ranged in size from 2.9-0.53 .times. 106 daltons, were synthesized in vitro by the holoenzyme. Transcript A appeared to be the major transcript since it was the size of the entire 20% of the genome shown in vivo to code for the early phage mRNA, it was one of the first transcripts synthesized at low enzyme-to-DNA molar ratios and it was synthesized in .apprx. 3 times the molar equivalent observed for the other transcripts. The A transcript initated primarily with GTP although a portion was also labeled with ATP. The B, C and D transcripts were present in equivalent molar ratios, were all smaller than transcript A, and were found to yield RNase III digestion products that were subsets of each other as well as of transcript A. Each of these transcripts proved to be a de novo transcript since each could be pulse labeled during the initial 20 s of the reaction and each transcript contained a triphosphate at its 5'' terminus. Evidently, the B and C transcripts initiate at or near the major A promoter but terminate at different termination or pause sites within the early region of the phage genome. Trancript D appears to initiate at a minor promoter within the terminally redundant region of the gemone preceding the A promoter.