N6-Acetyl-L-lysine is an acetylated amino acid. Post-translational lysine-acetylation is one of two major modifications of lysine residues in various proteins. Acetylation of specific lysine residues in the N-terminal domains of core histones is a biochemical marker of active genes. Acetylation is now known to play a major role in eukaryotic transcription. Specifically, acetyltransferase enzymes that act on particular lysine side chains of histones and other proteins are intimately involved in transcriptional activation. By modifying chromatin proteins and transcription-related factors, these acetylases are believed to regulate the transcription of many genes. The best-characterized mechanism is acetylation, catalyzed by histone acetyltransferase (HAT) enzymes. HATs function enzymatically by transferring an acetyl group from acetyl-coenzyme A (acetyl-CoA) to the amino group of certain lysine side chains within a histone's basic N-terminal tail region. Within a histone octamer, these regions extend out from the associated globular domains, and in the context of a nucleosome, they are believed to bind the DNA through charge interactions (positively charged histone tails associated with negatively charged DNA) or mediate interactions between nucleosomes. Lysine acetylation, which neutralizes part of a tail region's positive charge, is postulated to weaken histone-DNA or nucleosome-nucleosome interactions and/or signal a conformational change, thereby destabilizing nucleosome structure or arrangement and giving other nuclear factors, such as the transcription complex, more access to a genetic locus. In agreement with this is the fact that acetylated chromatin has long been associated with states of transcriptional activation. Specific recognition of N-acetyl-L-lysine is a conserved function of all bromodomains found in different proteins, recognized as an emerging intracellular signalling mechanism that plays critical roles in regulating gene transcription, cell-cycle progression, apoptosis, DNA repair, and cytoskeletal organization.