Methylation of histone H3 by coactivator-associated arginine methyltransferase 1

The preferential in vitro methylation of histone H3 by coactivator-associat ed arginine methyltransferase 1 (CARM1) has been proposed as a basis for it s ability to enhance gene transcription [Chen, D., et al. (1999) Science 28 4, 2174-2177]. To further evaluate the significance of H3 methylation, we s tudied the kinetics and site specificity of its modification by CARM1. Affi nity-purified CARM1 methylated recombinant chick H3, which is free of postt ranslational modifications, and calf thymus H3, which is heterogeneous with regard to preexisting modifications, equally well, exhibiting a V-max of 4 500 pmol min(-1) (mg of enzyme)(-1) and an apparent K-m for H3 of less than or equal to0.2 muM. The catalytic efficiency (k(cat)/K-m) of CARM 1 toward H3 was at least 1000 times that toward R1 (GGFGG (R) over bar GGFGG-amide) , a highly effective substrate for protein arginine methyltransferase 1. Pe ptide mapping of H-3-methyl-labeled H3 indicated methylation at Arg-2, Arg- l7, and Arg-26 in the N-terminal region and at one or more of four arginine s (128/129/131/134) at the C-terminus. Two of the N-terminal sites, Arg-17 and Arg-26, occur in the sequence KAX (R) over barK and appear to be more e fficiently methylated than Arg-2, CARM1 catalyzed formation of N-G,N-G- dim ethylarginine (asymmetric) but little or no N-G,N-G-dimethylarginine (symme tric) and no form of methyllysine. Amino acid analysis of untreated calf th ymus H3 revealed that 3.7% of the molecules naturally contain asymmetric di methylarginine and/or monomethylarginine, Our findings support the hypothes is that methylation of H3 may be involved in the mechanism of transcription al coactivation by CARM1 of genes whose expression is under the control of nuclear receptors.