Figure 4.

Lysine 4 is a major site of active H3 methylation in Tetrahymena and HeLa cells. (A) RP-HPLC-purified H3 isolated from ³H-AdoMet-labeled macronuclei was subjected to N-terminal automated sequencing and ³H radioactivity eluted from each cycle was counted. Amino acids identified at each cycle of microsequencing are listed; numbers correspond to the known positions of lysine residues. * denotes the position of a second, relatively minor peak of methylation occurring at lysine 27. The inset corresponds to RP-HPLC analysis of lysines 4 and 9 from the above sequencing run showing the positions of mono- or unmethylated lysine. (B) RP-HPLC purified H3.1 and H4 isolated from ³H-AdoMet-labeled HeLa cell nuclei was subjected to N-terminal automated sequencing and ³H radioactivity eluted from each cycle was counted. Analysis was as in A.