Diverse classes of non-coding RNAs, including snRNAs (small nuclear RNAs), play fundamental regulatory roles in gene expression. For example, 7SK RNA and the components of the splicing apparatus U1–U6 snRNAs are implicated in the regulation of transcriptional elongation. The first evidence for the involvement of RNA in the regulation of transcriptional initiation is now emerging. TFIIH (transcription factor IIH), a general transcription initiation factor, appears to associate specifically with U1 snRNA, a core splicing component. Reconstituted transcription in vitro demonstrates an increase in the rate of formation of the first phosphodiester bond by RNA polymerase II in presence of U1 snRNA. Reconstituted re-initiation is also stimulated by U1 snRNA. These results suggest that U1 snRNA functions in the regulation of transcription by RNA polymerase II in addition to its role in RNA processing. The implications of these data extend to the development of new technologies that will allow the identification and analysis of diverse RNA species present as regulatory components in transcription-related ribonucleoprotein complexes.

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