FIGURE 4.

H2Aub inhibits PRC2 MTase activity on mononucleosomes. A, DTT titration of PRC2 MTase activity on unmodified mononucleosomes (unmod nucl) as quantitated by scintillation counting of incorporated ³H. Error bars represent the S.D. of multiple scintillation counts. B and C, PRC2 MTase activity was tested under reducing conditions on Xenopus unmodified, H2Bub(G76A), and H2Aub(G76A) mononucleosomes. Representative experiments are shown. Reactions were separated by SDS-PAGE and Coomassie Blue-stained, and activity was assessed by fluorography. In B, a short exposure is shown below a longer exposure. In C, automethylation activity is indicated (*). Activity was also assessed by scintillation counting of incorporated ³H into a fraction of each reaction (one-half in A and one-fourth in B). Error bars indicate the S.D. of multiple scintillation counts of the same reaction. In C, **, p < 0.0001 (Student's paired test).