Gene 1.7 of bacteriophage T7 confers sensitivity of phage growth to dideoxythymidine

Ngoc Q. Tran, Lisa F. Rezende, Udi Qimron, Charles C. Richardson, Stanley Tabor

Research output: Contribution to journalArticlepeer-review


Bacteriophage T7 DNA polymerase efficiently incorporates dideoxynucleotides into DNA, resulting in chain termination. Dideoxythymidine (ddT) present in the medium at levels not toxic to Escherichia coli inhibits phage T7. We isolated 95 T7 phage mutants that were resistant to ddT. All contained a mutation in T7 gene 1.7, a nonessential gene of unknown function. When gene 1.7 was expressed from a plasmid, T7 phage resistant to ddT still arose; analysis of 36 of these mutants revealed that all had a single mutation in gene 5, which encodes T7 DNA polymerase. This mutation changes tyrosine-526 to phenylalanine, which is known to increase dramatically the ability of T7 DNA polymerase to discriminate against dideoxynucleotides. DNA synthesis in cells infected with wild-type T7 phage was inhibited by ddT, suggesting that it resulted in chain termination of DNA synthesis in the presence of gene 1.7 protein. Overexpression of gene 1.7 from a plasmid rendered E. coli cells sensitive to ddT, indicating that no other T7 proteins are required to confer sensitivity to ddT.

Original languageEnglish
Pages (from-to)9373-9378
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number27
StatePublished - 8 Jul 2008
Externally publishedYes


  • DNA metabolism
  • Deoxynucleotide kinase
  • Dideoxynucleosides
  • T7 DNA polymerase
  • Thymidine kinase


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