Genetic code expansion in stable cell lines enables encoded chromatin modification

Genetically encoded unnatural amino acids provide powerful strategies for modulating the molecular functions of proteins in mammalian cells. However this approach has not been coupled to genome-wide measurements, because efficient unnatural amino acid incorporation is limited to readily transfectable cells and leads to very heterogeneous expression. We demonstrate that rapid piggybac integration of the orthogonal pyrrolysyl-tRNA synthetase (PylS)/tRNAPyl CUA pair (and its derivatives) into the mammalian genome enables efficient, homogeneous unnatural amino acid incorporation into target proteins in diverse cells, and we reveal the distinct transcriptional responses of ES cells and MEFs to amber suppression. Genetically encoding Ne-acetyl-lysine in place of six lysine residues in histone H3, that are known to be post-translationally acetylated, enables deposition of pre-acetylated histones into cellular chromatin, via a synthetic pathway that is orthogonal to enzymatic modification, allowing us to determine the consequences of acetylation at specific amino acids in histones on gene expression. Overall design: mRNA was sequenced using polyA-enrichment and Truseq library preparation protocol. Two biological replicates were sequences for each cell line and condition

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Elsässer SJ, Ernst RJ, Walker OS, Chin JW