Murine histone acetyltransferases and deacetylases: Identification of nucleolar enzymes and interacting proteins

In eukaryotic cells DNA is associated with conserved basic proteins to form chromatin. The basic repeating subunit of chromatin is the nucleosome. While nucleosomes were long thought to be repressive, structures, incompatible with nuclear processes, like DNA replication or transcription, it has been recognized during the past decade, that nucleosomes and hence chromatin structure is an important and essential element of regulation. The N-terminal extensions of core histones (H4, H3, H2A, H2B) are subject to posttranslational acetylation of amino groups of side chains of specific and highly conserved lysine residues. This reversible modification is established and maintained by histone acetyltransferases and histone deacetylases. During the past three years, numerous genes encoding these enzymes have been identified as transcriptional regulators in yeast, plants and mammalian cells. In plants, our laboratory could identify a novel class of histone deacetylases, which represents phosphoproteins located in the nucleolus, with homology to a variety of nucleolar proteins and a class of rotamases, the peptidyl-prolyi-cis-trans isomerases. There are evidences from plant cells that these nucleolar histone deacetylases are involved in the regulation of ribosomal DNA transcription. Members of this novel class of deacetylases are also present in fungi. Based on promising pilot experiments we present a project that deals with the identification and characterization of a murine homolog of the nucleolar type of deacetylase. Moreover, we want to characterize all histone acetyltransferases and deacetylases that are specifically involved in nucleolar chromatin modification and we will identify proteins of the ribosomal chromatin compartment that interact with different types of acetyltransferases and deacetylases. The final aim of the project is to gain an understanding of the impact of histone acetylation for ribosomal gene replication and transcription during growth and differentiation of murine cells.