Replication of RNA by the DNA-dependent RNA polymerase of phage T7

Cell. 1989 May 5;57(3):423-31. doi: 10.1016/0092-8674(89)90917-3.


The DNA-dependent RNA polymerase of bacteriophage T7 utilizes a specific RNA as a template and replicates it efficiently and accurately. The RNA product (X RNA), approximately 70 nucleotides long, is initiated with either pppC or pppG and contains an AU-tich sequence. Replication of X RNA involves synthesis of complementary strands. Both strands are also significantly self-complementary, producing RNA with an extensive hairpin secondary structure. Replication of X RNA by T7 RNA polymerase is both template and enzyme specific. No other RNA serves as template for replication; neither do other polymerases, including the closely related T3 RNA polymerase, replicate X RNA. The T7 RNA polymerase-X RNA system provides an interesting model for studying replication of RNA by DNA-dependent RNA polymerases. Such a mechanism has been proposed to propagate viroids and hepatitis delta, pathogenic RNAs whose replication seems to depend on cellular RNA polymerases.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / physiology*
  • RNA, Viral / biosynthesis
  • RNA, Viral / genetics*
  • T-Phages / enzymology*
  • T-Phages / genetics
  • Transcription, Genetic
  • Virus Replication


  • RNA, Viral
  • DNA-Directed RNA Polymerases