S. Rea is the first author of a 2000 study identifying SUV39H1 and its mouse counterpart as histone methyltransferases with a specific target: lysine 9 near the beginning of histone H3. In experiments outside living biological cells, these enzymes transferred methyl groups to that position. Mapping the catalytic activity implicated the SET domain together with neighboring regions rich in cysteine.[ref]
The specificity is the important idea: a histone modification has an address within a protein, rather than simply changing the bulk composition of chromatin. The study also found that modification of lysine 9 interfered with phosphorylation of neighboring serine 10, illustrating how nearby chemical changes can interact. Experiments that altered the enzymes' activity in biological cells also changed histone H3 phosphorylation and produced abnormal divisions. These observations helped connect a defined catalytic reaction with the regulation of chromatin; they did not imply that every modified histone has the same effect in every biological context.[ref]
Regulation of chromatin structure by site-specific histone H3 methyltransferases by S. Rea and others. abstract, catalytic mapping and modification interdependence
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