Mutations induced by bacteriophage T7 RNA polymerase and their effects on the composition of the T7 genome

Anton Beletskii, Andrei Grigoriev, Susan Joyce, Ashok S. Bhagwat

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


We show here that transcription by the bacteriophage T7 RNA polymerase increases the deamination of cytosine bases in the non-transcribed strand to uracil, causing C to T mutations in that strand. Under optimal conditions, the mutation frequency increases about fivefold over background, and is similar to that seen with the Escherichia coli RNA polymerase. Further, we found that a mutant T7 RNA polymerase with a slower rate of elongation caused more cytosine deaminations than its wild-type parent. These results suggest that promoting cytosine deamination in the non-transcribed strand is a general property of transcription in E. coli and is dependent on the length of time the transcription bubble stays open during elongation. To see if transcription-induced mutations have influenced the evolution of bacteriophage T7, we analyzed its genome for a bias in base composition. Our analysis showed a significant excess of thymine over cytosine bases in the highly transcribed regions of the genome. Moreover, the average value of this bias correlated well with the levels of transcription of different genomic regions. Our results indicate that transcription-induced mutations have altered the composition of bacteriophage T7 genome and suggest that this may be a significant force in genome evolution. (C) 2000 Academic Press.

Original languageEnglish (US)
Pages (from-to)1057-1065
Number of pages9
JournalJournal of molecular biology
Issue number5
StatePublished - Jul 28 2000
Externally publishedYes

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


  • Cytosine deamination
  • Mutagenesis
  • Spontaneous mutations
  • Transcription
  • Uracil


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