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

Transcription of the Caulobacter crescentus phage phi Cd1 genome requires both the host RNA polymerase and a phage-encoded, rifampicin-resistant RNA polymerase. Transcription of the early region of the phi 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 X 10(6) to 0.53 X 10(6) daltons, were synthesized in vitro by the holoenzyme. Transcript A appeared to be the major transcript since (a) it was the size of the entire 20% of the genome shown in vivo to code for the early phage mRNA, (b) it was one of the first transcripts synthesized at low enzyme-to-DNA molar ratios, and (c) it was synthesized in approximately 3 times the molar equivalent observed for the other transcripts. The A transcript initiated 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 (a) each could be pulse labeled during the initial 20 s of the reaction and (b) each transcript contained a triphosphate at its 5' terminus. Evidence is presented that suggests that 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. Transcript D appears to initiate at a minor promoter within the terminally redundant region of the genome preceding the A promoter.