Gcn5 and NuA4 lysine acetyltransferases cooperatively promote DNA replication

Abstract

Eukaryotic cells must replicate DNA within the confines of chromatin. The basic unit of chromatin is the nucleosome, which consists of approximately 147 base pairs of DNA wrapped around an octamer of histone proteins. Because chromatin is generally inhibitory to mechanisms requiring a DNA template, enzymes that modify nucleosomes have evolved. Post-translational histone modifications can influence all DNA-dependent processes, including replication, which is initiated at sites called origins. Acetylation of histone lysine tails is catalyzed by lysine acetyltransferases, or KATs. The work of this thesis presents evidence that the cooperative action of two KATs, Gcn5 and NuA4, combine in the budding yeast <italic>Saccharomyces cerevisiae</italic> to promote replication origin firing. Inducible knock-down of Gcn5 results in reduced levels of BrdU incorporation at replication origins during S-phase, and BrdU levels are further reduced with the addition of <italic>eaf5δ</italic>, a deletion allele of a subunit of the NuA4 KAT complex. Gcn5 and NuA4 are also required for efficient growth of <italic>7oriδ</italic>, a yeast strain with an origin-deficient chromosome. Although replication origins have been deleted in the <italic>7oriδ</italic> strain, de novo origin firing can still occur at these sites. These results show that the combined action of Gcn5 and NuA4 KAT enzymes play critical roles in replication, and that origin identity in <italic>S. cerevisiae</italic> possesses surprising plasticity.