The DNA of eukaryotic cells is organized in a complex with proteins, either as interphase chromatin or mitotic chromosomes. Nucleosomes, the structural subunits of chromatin, have long been considered as static structures, incompatible with processes occurring in chromatin. During the past few years it has become evident that the histone part of the nucleosome has important regulatory functions. Some of these functions are mediated by the N-terminal core histone domains which contain sites for posttranslational modifications, among them lysine residues for reversible acetylation. Recent results indicate that acetylation and deacetylation of N-terminal lysines of nucleosomal core histones represent a means of molecular communication between chromatin and the cellular signal transduction network, resulting in heritable epigenetic information. Data on enzymes involved in acetylation and the pattern of acetylated lysine sites on chromosomes, as well as genetic data on yeast transcriptional repression, suggest that acetylation may lead to structural transitions as well as specific signalling within distinct chromatin domains.