Mediator is essential for small nuclear and nucleolar RNA transcription in yeast

Abstract

Eukaryotic RNA polymerase II (RNAPII) transcribes mRNA genes as well as non-protein coding RNAs (ncRNAs) including small nuclear and nucleolar RNAs (sn/snoRNAs). In metazoans, RNAPII transcription of sn/snoRNAs is facilitated by a number of specialized complexes, but no such complexes have been discovered in yeast. It has thus been proposed that yeast sn/snoRNA promoters use the same complement of factors as mRNA promoters, but the extent to which key regulators of mRNA genes act at sn/snoRNA genes in yeast is unclear. Here, we investigated a potential role for the Mediator complex, essential for mRNA gene transcription, in the transcription of sn/snoRNA genes. We found that the complete Mediator complex maps to most sn/snoRNA gene regulatory regions and that loss of Mediator function results in a robust reduction in RNAPII and TFIIB occupancy at sn/snoRNA genes. Furthermore, deletion of subunits of the activator-interacting Mediator tail module does not affect Mediator recruitment to, or transcription of, sn/snoRNAs. Taken together, our analyses indicate that Mediator promotes PIC formation and transcription at sn/snoRNA genes, expanding the role of this critical regulator beyond its known functions in mRNA gene transcription and demonstrating further mechanistic similarity between the transcription of mRNA and sn/snoRNA genes.