Fig. 1. MES-4 is a histone methyltransferase for H3K36. (A) MES-4 has HMT activity in vitro. Bacterially expressed His-tagged MES-4 was incubated with chicken oligonucleosomes and S-adenosyl-L-[methyl-³H] methionine. The reaction products were analyzed by SDS-PAGE followed by fluorography (top panel) and Coomassie staining (middle panel). Western blots (bottom panel) were performed on the soluble extracts to detect MES-4. Asterisks mark H3 breakdown products in lane 4. (B-I) H3K36me2 is undetectable in mes-4(bn73) hermaphrodite germ lines and early embryos. Chromatin (labeled DNA) stained with PA3, red; H3K36me2 staining, green. Arrowheads mark somatic nuclei; arrows indicate X chromosomes. (B,C) Wild-type and mes-4 distal gonads. (D,E) Wild-type and mes-4 pachytene nuclei. (F,G) Wild-type and mes-4 oocytes. (H,I) Wild-type and mes-4 one-cell embryos. Anterior is to the left. Asterisks mark polar bodies. Scale bars: 10 µm.