RNA polymerase II acts as an RNA‐dependent RNA polymerase to extend and destabilize a non‐coding RNA

RNA polymerase II (Pol II) is a well‐characterized DNA‐dependent RNA polymerase, which has also been reported to have RNA‐dependent RNA polymerase (RdRP) activity. Natural cellular RNA substrates of mammalian Pol II, however, have not been identified and the cellular function of the Pol II RdRP activity is unknown. We found that Pol II can use a non‐coding RNA, B2 RNA, as both a substrate and a template for its RdRP activity. Pol II extends B2 RNA by 18 nt on its 3′‐end in an internally templated reaction. The RNA product resulting from extension of B2 RNA by the Pol II RdRP can be removed from Pol II by a factor present in nuclear extracts. Treatment of cells with α‐amanitin or actinomycin D revealed that extension of B2 RNA by Pol II destabilizes the RNA. Our studies provide compelling evidence that mammalian Pol II acts as an RdRP to control the stability of a cellular RNA by extending its 3′‐end.     

Antisense regulation by transposon‐derived RNAs in the hyperthermophilic archaeon Sulfolobus solfataricus

We report the first example of antisense RNA regulation in a hyperthermophilic archaeon. In Sulfolobus solfataricus, the transposon‐derived paralogous RNAs, RNA‐257_1–4, show extended complementarity to the 3′ UTR of the 1183 mRNA, encoding a putative phosphate transporter. Phosphate limitation results in decreased RNA‐257₁ and increased 1183 mRNA levels. Correspondingly, the 1183 mRNA is faster degraded in vitro upon duplex formation with RNA‐257₁. Insertion of the 1183 3′ UTR downstream of the lacS gene results in strongly reduced lacS mRNA levels in transformed cells, indicating that antisense regulation can function in trans.