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PLoS Genet. 2011 Jul;7(7):e1002195. doi: 10.1371/journal.pgen.1002195. Epub 2011 Jul 21.

SHH1, a homeodomain protein required for DNA methylation, as well as RDR2, RDM4, and chromatin remodeling factors, associate with RNA polymerase IV.

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1
Department of Molecular, Cell, and Developmental Biology, University of California Los Angeles, Los Angeles, California, United States of America.

Abstract

DNA methylation is an evolutionarily conserved epigenetic modification that is critical for gene silencing and the maintenance of genome integrity. In Arabidopsis thaliana, the de novo DNA methyltransferase, domains rearranged methyltransferase 2 (DRM2), is targeted to specific genomic loci by 24 nt small interfering RNAs (siRNAs) through a pathway termed RNA-directed DNA methylation (RdDM). Biogenesis of the targeting siRNAs is thought to be initiated by the activity of the plant-specific RNA polymerase IV (Pol-IV). However, the mechanism through which Pol-IV is targeted to specific genomic loci and whether factors other than the core Pol-IV machinery are required for Pol-IV activity remain unknown. Through the affinity purification of nuclear RNA polymerase D1 (NRPD1), the largest subunit of the Pol-IV polymerase, we found that several previously identified RdDM components co-purify with Pol-IV, namely RNA-dependent RNA polymerase 2 (RDR2), CLASSY1 (CLSY1), and RNA-directed DNA methylation 4 (RDM4), suggesting that the upstream siRNA generating portion of the RdDM pathway may be more physically coupled than previously envisioned. A homeodomain protein, SAWADEE homeodomain homolog 1 (SHH1), was also found to co-purify with NRPD1; and we demonstrate that SHH1 is required for de novo and maintenance DNA methylation, as well as for the accumulation of siRNAs at specific loci, confirming it is a bonafide component of the RdDM pathway.

PMID:
21811420
PMCID:
PMC3141008
DOI:
10.1371/journal.pgen.1002195
[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

The authors have declared that no competing interests exist.

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