Mediator directs co-transcriptional heterochromatin assembly by RNA interference-dependent and -independent pathways

PLoS Genet. 2013;9(8):e1003677. doi: 10.1371/journal.pgen.1003677. Epub 2013 Aug 15.

Abstract

Heterochromatin at the pericentromeric repeats in fission yeast is assembled and spread by an RNAi-dependent mechanism, which is coupled with the transcription of non-coding RNA from the repeats by RNA polymerase II. In addition, Rrp6, a component of the nuclear exosome, also contributes to heterochromatin assembly and is coupled with non-coding RNA transcription. The multi-subunit complex Mediator, which directs initiation of RNA polymerase II-dependent transcription, has recently been suggested to function after initiation in processes such as elongation of transcription and splicing. However, the role of Mediator in the regulation of chromatin structure is not well understood. We investigated the role of Mediator in pericentromeric heterochromatin formation and found that deletion of specific subunits of the head domain of Mediator compromised heterochromatin structure. The Mediator head domain was required for Rrp6-dependent heterochromatin nucleation at the pericentromere and for RNAi-dependent spreading of heterochromatin into the neighboring region. In the latter process, Mediator appeared to contribute to efficient processing of siRNA from transcribed non-coding RNA, which was required for efficient spreading of heterochromatin. Furthermore, the head domain directed efficient transcription in heterochromatin. These results reveal a pivotal role for Mediator in multiple steps of transcription-coupled formation of pericentromeric heterochromatin. This observation further extends the role of Mediator to co-transcriptional chromatin regulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Centromere / genetics
  • Chromatin Assembly and Disassembly / genetics
  • Gene Expression Regulation, Fungal
  • Heterochromatin / genetics*
  • RNA Polymerase II / genetics*
  • RNA Polymerase II / metabolism
  • RNA, Small Interfering / genetics
  • RNA, Untranslated / genetics
  • RNA, Untranslated / metabolism
  • Schizosaccharomyces / genetics*
  • Schizosaccharomyces pombe Proteins / genetics*
  • Schizosaccharomyces pombe Proteins / metabolism
  • Transcription, Genetic*

Substances

  • Heterochromatin
  • RNA, Small Interfering
  • RNA, Untranslated
  • Schizosaccharomyces pombe Proteins
  • RNA Polymerase II

Associated data

  • GEO/GSE43543

Grants and funding

YM was supported by a Grant-in-Aid for Scientific Research (A) from the Japan Society for the Promotion of Science and by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. EO was a Research Fellow of the Japan Society for the Promotion of Science and was supported by the JSPS Global COE program (project no. B01). HK was supported by a grant-in-aid for Scientific Research and a grant from the JST PRESTO program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.