SET3p monomethylates histone H3 on lysine 9 and is required for the silencing of tandemly repeated transgenes in Chlamydomonas

J. Armando Casas-Mollano, Karin van Dijk, John Eisenhart, Heriberto Cerutti

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

SET domain-containing proteins of the SU(VAR)3-9 class are major regulators of heterochromatin in several eukaryotes, including mammals, insects, plants and fungi. The function of these polypeptides is mediated, at least in part, by their ability to methylate histone H3 on lysine 9 (H3K9). Indeed, mutants defective in SU(VAR)3-9 proteins have implicated di- and/or trimethyl H3K9 in the formation and/or maintenance of heterochromatin across the eukaryotic spectrum. Yet, the biological significance of monomethyl H3K9 has remained unclear because of the lack of mutants exclusively defective in this modification. Interestingly, a SU(VAR)3-9 homolog in the unicellular green alga Chlamydomonas reinhardtii, SET3p, functions in vitro as a specific H3K9 monomethyltransferase. RNAi-mediated suppression of SET3 reactivated the expression of repetitive transgenic arrays and reduced global monomethyl H3K9 levels. Moreover, chromatin immunoprecipitation (ChIP) assays demonstrated that transgene reactivation correlated with the partial loss of monomethyl H3K9 from their chromatin. In contrast, the levels of trimethyl H3K9 or the repression of euchromatic sequences were not affected by SET3 downregulation; whereas dimethyl H3K9 was undetectable in Chlamydomonas. Thus, our observations are consistent with a role for monomethyl H3K9 as an epigenetic mark of repressed chromatin and raise questions as to the functional distinctiveness of different H3K9 methylation states.

Original languageEnglish (US)
Pages (from-to)939-950
Number of pages12
JournalNucleic acids research
Volume35
Issue number3
DOIs
StatePublished - Feb 1 2007

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Chlamydomonas
Transgenes
Histones
Lysine
Heterochromatin
Chromatin
Chlamydomonas reinhardtii
Chlorophyta
Chromatin Immunoprecipitation
RNA Interference
Eukaryota
Epigenomics
Methylation
Insects
Mammals
Fungi
Down-Regulation
Maintenance
Peptides
SU(VAR)3-9

ASJC Scopus subject areas

  • Genetics

Cite this

SET3p monomethylates histone H3 on lysine 9 and is required for the silencing of tandemly repeated transgenes in Chlamydomonas. / Casas-Mollano, J. Armando; van Dijk, Karin; Eisenhart, John; Cerutti, Heriberto.

In: Nucleic acids research, Vol. 35, No. 3, 01.02.2007, p. 939-950.

Research output: Contribution to journalArticle

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