Expression of Histone H3 Tails with Combinatorial Lysine Modifications under the Reprogrammed Genetic Code for the Investigation on Epigenetic Markers

We report the ribosomal synthesis of N-terminal peptides of histone H3, so-called H3 tail (H3t), with combinatorial methyl and acetyl modifications of selected lysine residues, and the application of such peptides to studying the influence of lysine modification on H3t binding to chromodomain of heterochromatin protein 1 (chromoHP1). Genetic code reprogramming was employed to reassign four codons to acetylated, mono-, di-, and trimethylated lysines, and 38-mer H3t peptides containing modified lysines at designated sites were expressed from the corresponding mRNA sequences. Using a series of H3t constructs, we show complex crosstalk among methylated lysine 9 and 27, and acetylated lysine 14 for binding to chromoHP1. This proof-of-concept study offers a unique means for the synthesis of not only an H3t library containing modified lysines but also other classes of peptides bearing posttranslational methylation and acetylation.