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Mol Cell. 2002 Dec;10(6):1417-27.

Cellular RNA-dependent RNA polymerase involved in posttranscriptional gene silencing has two distinct activity modes.

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Department of Biosciences and Institute of Biotechnology, University of Helsinki, P.O. Box 56, 5, FIN-00014, Viikinkaari, Finland.


Recent genetic data suggest that proteins homologous to a plant RNA-dependent RNA polymerase (RdRP) play a central role in posttranscriptional gene silencing (PTGS) in many organisms. We show here that purified recombinant protein QDE-1, a genetic component of PTGS ("quelling") in the fungus Neurospora crassa, possesses RNA polymerase activity in vitro. The full-length enzyme and its enzymatically active C-terminal fragment perform two different reactions on single-stranded RNA templates, synthesizing either extensive RNA chains that form template-length duplexes or approximately 9-21-mer complementary RNA oligonucleotides scattered along the entire template. QDE-1 supports both de novo and primer-dependent initiation mechanisms. These results suggest that several distinct activities of cell-encoded RdRPs can be employed for efficient PTGS in vivo.

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