Transcriptional regulation of three double-stranded RNA segments of bacteriophage phi 6 in vitro

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Abstract
Three double-stranded RNA segments of bacteriophage .vphi.6 (L, M and S) were transcribed in vitro by a virion-associated RNA polymerase. Regulation of L transcription was distinct from regulation of M and S transcription. Transcription of the L segment, which codes for early proteins, required Mn2+ and high concentrations of all 4 ribonucleoside triphosphates and was inhibited by polyamines such as spermine. Transcription of the M and S segments, which code for late proteins, required Mn2+ or Mn2+ ion and relatively low concentrations of all ribonucleoside triphosphates except GTP and was enhanced by polyamines. Optimal conditions for L transcription were more stringent than those for M and S transcription. These 2 apparently different patterns produced in in vitro transcription presumably reflect the 2 distinct in vivo transcription patterns; i.e., similar amounts of 3 single-stranded RNA species were transcribed from the 3 corresponding segments of double-stranded RNA (early pattern) and a much larger amont of single-stranded RNA species was transcribed from M and S segments than from the L segment (late pattern). The early transcription pattern may be changed into the late pattern by a change of environment, such as substrate concentration. This suggests that the different enzymatic properties under the different environmental conditions of the virion-associated transcriptase are responsible for the transcriptional regulation throughout the infection cycle of bacteriophage .vphi.6.