= H3K27 methylation
{c}
<H3K27 methylation> is addition of one or more <methyl groups> to the side chain of <lysine> 27 in <histone H3>. Mono-, di- and trimethylated states are different chemical states; a measurement of one is not automatically a measurement of the others. <H3K27 trimethylation> is particularly associated with Polycomb-mediated <gene silencing>. <Histone methyltransferase activity associated with a human multiprotein complex containing the Enhancer of Zeste protein by Andrei Kuzmichev and others>[2002, abstract: purified PRC2 and SET-domain-dependent histone methyltransferase activity]{ref}
A mechanistic test distinguishes correlation from <catalysis>. A purified complex can be supplied with <histones> and a methyl donor to test transfer, while changing a catalytic region tests whether that activity depends on an intact <enzyme>. In a <cell>, the distribution of the mark also depends on recruitment, removal and replacement of <histones>, not only on total <enzyme> abundance.
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