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. 2015 Feb 3;10(2):122–126. doi: 10.1080/15592294.2014.1003750

Figure 1.

Figure 1.

Model of the possible role of H2Bub during DNA replication stress. (A) Ubiquitylation (Ub; pink stars) of H2B by Bre1 (red rectangle) may facilitate chromatin reassembly under replication stress, thereby delaying progression of the replisome, which consists of DNA Polymerase I (blue triangle, P) and the Mcm2–7 helicase (purple oval), among other proteins. This serves to preserve the stability of the replication fork until it can be repaired. Increased assembly of nucleosomes (composed of 8 histones, shown as yellow circles) behind the replisome may also facilitate recruitment of the helicase Sgs1 (required to unwind DNA structures generated during DNA repair; shown as a blue rectangle) and phosphorylation of Rad53 (green oval), thereby further enhancing stability of the fork. Phosphorylated Rad53 dissociates from the histone chaperone Asf1 (gray hexagon), enabling the latter to deposit acetylated H3/H4 onto DNA (blue lines). (B) In cells lacking H2Bub, movement of the replication fork is less restricted, which results in the formation of shorter tracts of single-stranded DNA coated with RPA (orange circles). This reduces Sgs1 recruitment, and delays Rad53 phosphorylation.