Histones H1 and H3 compete for SET7/9-dependent methylation. (A) H3 and H1 compete for methylation by SET7/9. H1 was methylated in presence of the indicated molar ratios of H3. In lanes 6 and 7, H3 was incubated with ARTD1 and NAD+ in the presence or absence of 3-AB before addition of H1 and the methylation reaction. (B) ARTD1 was auto-modified for the indicated times and then inhibited by addition of PJ-34. H1 was added to the reaction either before or after the PARylation. Methylation was started after addition of PJ-34 by adding SET7/9 and 14C-SAM. (C) As for (B), but a histone mix was used.