The major innovation in chromatin regulation: chemical modifications serve as signals

Lots of individual site-specific histone modifications are described in the literature. Tough, the mechanism and functional role of chromatin regulation is substantially less well understood. Some of the open fundamental questions are: Is there a complex chromatin code? How much information can chromatin hold on top of the genetic information? How does transcriptional regulation by chromatin and transcription factors conceptually differ?

To address these questions, we studied chromatin regulation in the light of evolution. We, therefore, considered the phylogenetic distribution of functional domains involved in chromatin regulation. We could derive the hypothesis that the functional role of chromatin is general regulation and specification of genomic states that correspond to phenotypic states. Variants of chromosomal architectural proteins serve this function in all domains of life. Only Archaea and Eukaryotes seem to modify their DNA associated proteins to change their chemical properties and affinity to DNA in response to differential regulation. The major innovation in chromatin regulation, however, is the appearance of 8 structurally distinct domain families that bind specific modifications. With the emergence of these "reader" molecules, modifications start to serve as signal in an information theoretic sense.

In my talk I will present our hypothesis on chromatin evolution and discuss the conceptual and functional consequences that can serve as a framework to pose and answer biological questions and to explain regulatory phenomena that have already been observed.