Abstract
Modification of the histone proteins H4 and H3 occurs before changes in chromatin architecture. Whereas histone acetylation leads to greater DNA accessibility and transcription, histone methylation can also regulate the higher ordered structure of chromatin. Little is known of the mammalian proteins involved in the methylation of histones; however, Rea et al . have now identified a human protein termed SUV39H1 that methylates H3. In vitro methylation assays revealed that Lys 9 , located in the NH 2 -terminus of H3, is methylated in the presence of SUV39H1. Prior acetylation of Lys 9 blocked Lys 9 methylation, and phosphorylation of Ser 10 blocked the ability of SUV39H1 to methylate Lys 9 in vitro. Reciprocally, prior methylation of Lys 9 decreased the ability of aurora kinase (which can phosphorylate Ser 10 in H3) to use H3 as a substrate. However, prior acetylation of Lys 9 (compared to an unacetylated control) increased the ability of aurora kinase to phosphorylate Ser 10 . This suggests that steric hindrance is not the reason that methylation and phosphorylation were antagonistic, but that H3 NH 2 -terminal modification events are interdependent. Fluorescence assays indicated that SUV39H-deficient cells had increased amounts of phosphorylated H3, supporting the observation that methylation of Lys 9 blocked the phosphorylation of Ser 10 . Thus, having local regions of phosphorylated, acetylated, or methylated histones may contribute to epigenetic heritability of DNA states. A News & Views article by Paro discusses the role of catalytic domains in methyltransferases and the importance of histone modification. Rea, S., Eisenhaber, F., O'Carroll, D., Strahl, B.D., Sun, Z.-W., Schmid, M., Opravil, S., Mechtler, K., Ponting, C.P., Allis, C.D., and Jenuwein, T. (2000) Regulation of chromatin structure by site-specific histone H3 methyltransferases. Nature 406 : 593-599. [Online Journal] Paro, R. (2000) Chromatin regulation: Formatting genetic text. Nature 406 : 579-580. [Online Journal]
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