The capped U6 small nuclear RNA is transcribed by RNA polymerase III.

U6 RNA is an abundant, capped, small nuclear RNA (snRNA) species associated with heterogeneous nuclear ribonucleoproteins in eukaryotic cells.U4 RNA and U6 RNA are hydrogen bonded in a 1:l ratio in discrete small nuclear ribonucleoprotein particles that are required in pre-mRNA processing.Previous reports have established that the mRNAs and U1 to US U-snRNAs are synthesized by RNA polymerase 11.Evidence is presented here for synthesis of U6 RNA by RNA polymerase 111.The synthesis of U6 RNA in vitro, using Novikoff hepatoma or HeLa whole cell extracts, was not inhibited at low (1 Irg/ml) concentrations of aamanitin, and only 36% inhibition occurred at 10 fig/ ml concentration.The in vitro synthesized U6 RNA, like other RNA polymerase I11 transcripts, was asso- ciated with La antigen.The U6 RNA synthesized in vitro by the whole cell extracts was capped, but no other internal post-transcriptional modifications were found.Uridylic acid residues were also added posttranscriptionally to the 3'-end of U6 RNA in vitro.U6 RNA, though capped on its €5'-end, is transcribed by RNA polymerase 111; this is the first report of a capped RNA molecule synthesized by RNA polymerase In.U6 RNA is one of the six abundant, capped, small nuclear RNAs.U6 RNA has been found in mammalian, avian, amphibian, insect, and dinoflagellate cells (Busch et aZ., 1982;