H2B K123 ubiquitination and H3 K4 methylation play a positive role in DNA replication

Abstract

DNA replication is initiated from sites in the genome known as origins of replication. In eukaryotic cells, control over the function of origins is essential to ensure complete genome replication, and its loss results in genome instability. Despite the importance of controlling origin function, little is known about the determinants of origin identity or the effects of chromatin structure on origin function. We hypothesize that unique elements of chromatin structure are responsible for defining functional origins and regulating replication initiation. Our objective is to characterize the effects of histone modifications on origin function using genetic and biochemical analyses. We have conducted a genetic screen to identify chromatin‐modifying enzymes that affect the licensing of origins. We discovered that loss of the Bre1 E3 ubiquitin ligase compromises the growth of a replication mutant. This enzyme, in conjunction with the E2 ubiquitin‐conjugating enzyme, Rad6, monoubiquitinates H2B K123, and this mark is a pre‐requisite for H3 K4 methylation. We are analyzing the mechanism by which these marks affect DNA replication. We will also determine whether the presence/absence of these marks affects recruitment of replication proteins, origin firing, or replication fork progression. These studies will provide a mechanistic view of how these and other histone modifications regulate DNA replication. (AHA 10PRE3740013, NIH 5R01GM083024‐02)