Abstract
In this chapter, we will present posttranslational modifications as a general mechanism for instructing proteins about their function. Moreover, they allow proteins to “memorize” their encounters, such as contacts with other proteins. Histone proteins are the key examples of this protein communication system. In particular, lysine acetylations and methylations of histone tails have a large functional impact. Genome-wide profiling of the large set of posttranscriptional histone modifications provides the basis of the histone code. This code leads to the understanding, how the epigenome directs transcriptional regulation and stores information. Histone modifying enzymes, such as HATs, HDACs, KMT and lysine demethylases (KDMs), either add or remove posttranslational modifications to histone proteins and in this way change the functional profile of the epigenome.