Requirement of CHROMOMETHYLASE3 for Maintenance of CpXpG Methylation
Anders M. Lindroth,1*
Xiaofeng Cao,1*
James P. Jackson,1*
Daniel Zilberman,1
Claire M. McCallum,3
Steven Henikoff,23
Steven
E. Jacobsen1
Epigenetic silenced alleles of the Arabidopsis SUPERMAN
locus (the clark kent alleles) are associated with dense
hypermethylation at noncanonical cytosines (CpXpG and asymmetric sites,
where X = A, T, C, or G). A genetic screen for suppressors of a
hypermethylated clark kent mutant identified nine
loss-of-function alleles of CHROMOMETHYLASE3
(CMT3), a novel cytosine methyltransferase homolog. These cmt3 mutants display a wild-type morphology but
exhibit decreased CpXpG methylation of the SUP gene and of
other sequences throughout the genome. They also show reactivated
expression of endogenous retrotransposon sequences. These results show
that a non-CpG DNA methyltransferase is responsible for maintaining epigenetic gene silencing.
1 Department of Molecular, Cell and
Developmental Biology, University of California, Los Angeles, CA 90095, USA.
2 Howard Hughes Medical Institute,
3 Fred Hutchinson Cancer Research Center, Seattle,
WA 98109, USA.
*
These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail:
jacobsen{at}ucla.edu
