| Chromosomes in eukaryotes are highly compacted during mitosis and meiosis thus ensuring proper segregation of genetic information in each nuclear division. Phosphorylation of histone H3 at serine 10 (Ser10) is tightly associated with the compacted chromosomes in a reversibly regulated manner. To analyze the function for H3 phosphorylation genetically, I chose budding yeast, Saccharomyces cerevisiae, as a model system and demonstrated that the pattern for H3 phosphorylation is evolutionarily conserved in this organism. A pair of genetically antagonistic enzymes, Ipl1 kinase and Glc7 phosphatase, were found to be required for maintaining proper H3 phosphorylation levels in vivo. Both enzymes are essential and are involved in various mitotic processes, although the casual relationship between their function and H3 phosphorylation is not established. Regulation of mitotic and meiotic H3 phosphorylation by this enzyme system was recapitulated in C. elegans. In a variety of human cancers, the Ipl1 homologue, aurora kinase, was found mis-regulated, implicating an important link between chromosome dynamics and human disease.;Numerous principles of histone functions in vivo have been established using yeast as a model system. These paradigms, however, were established upon systems in which only the histones within the histone dimer sets, i.e. H2A--H2B and H3--H4 can be analyzed. To gain a more comprehensive knowledge of the interplay between any given histones, I constructed an 'all-purpose' histone shuffle strain which allowed mutations of any given histones to be constructed in one strain. With it, I have ruled out the possibility that Ser10 phosphorylation of H3 is functionally redundant with other histone amino (N)-terminal domain (tail). Analyses of combined histone N-terminal tail deletions revealed surprisingly that yeast cells without both H2A and H2B N-terminal tails are viable. Furthermore, the N-terminus of H4 is involved in a broad spectrum of cellular processes whereas the H2B tail seems to be largely dispensable. Finally, N-terminal tails of H4 and H2A but not of H3 and H2B have significant roles in the cellular response to DNA damage. Future experiments are required to delineate the mechanism underlying these new observations and should be facilitated by this all-purpose histone shuffle strain. |
