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

Abstract

word count: 198 11 Introduction/results/discussion word count: 3,085 12 Materials and methods word count: 1,433 13 Abstract 14 Eukaryotic RNA polymerase II (RNAPII) transcribes mRNA genes as well as non-protein coding 15 RNAs (ncRNAs) including small nuclear and nucleolar RNAs (sn/snoRNAs). In metazoans, 16RNAPII transcription of sn/snoRNAs is facilitated by a number of specialized complexes, but no 17 such complexes have been discovered in yeast. It has thus been proposed that yeast 18 sn/snoRNA promoters use the same complement of factors as mRNA promoters, but the extent 19 to which key regulators of mRNA genes act at sn/snoRNA genes in yeast is unclear. Here, we 20 investigated a potential role for the Mediator complex, essential for mRNA gene transcription, in 21 the transcription of sn/snoRNA genes. We found that the complete Mediator complex maps to 22 most sn/snoRNA gene regulatory regions and that loss of Mediator function results in a robust 23 reduction in RNAPII and TFIIB occupancy at sn/snoRNA genes. Furthermore, deletion of 24 subunits of the activator-interacting Mediator tail module does not affect Mediator recruitment to, 25 or transcription of, sn/snoRNAs. Taken together, our analyses indicate that Mediator promotes 26 PIC formation and transcription at sn/snoRNA genes, expanding the role of this critical regulator 27 beyond its known functions in mRNA gene transcription and demonstrating further mechanistic 28 similarity between the transcription of mRNA and sn/snoRNA genes. 29