The paradoxical involvement of RNA-mediated gene silencing in the maintenance of some DNA silencing is bridged in Arabidopsis plants by an RNA polymerase that acts as a liaison between both pathways, UK researchers report in the February 3 issue of Science.

Alan Herr, from the John Innes Centre, Norwich, and colleagues from there and elsewhere show that an RNA polymerase connects RNA and DNA silencing pathways. They found that mutants in RNA polymerase IV (Pol IV, also called RPD1), part of a new clade of polymerases in plants, were defective in both pathways.

"The finding of a new silencing-specific RNA polymerase is a surprising twist in the evolution of RNA polymerases," Herr wrote The Scientist in an E-mail. "Even though Pol IV is plant specific, the function of Pol IV may be performed by another RNA polymerase in other programs. Silencing of a locus does not mean that...

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