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. Author manuscript; available in PMC: 2017 May 1.
Published in final edited form as: Trends Biochem Sci. 2016 Mar 17;41(5):434–445. doi: 10.1016/j.tibs.2016.02.005

Figure 4. Ribonucleotides both in DNA and R-loops contribute to genome instability.

Figure 4

In pol2M644G rnh1Δ rnh201Δ strains replication is impaired by the burden of ribonucleotides in leading strand DNA (represented as red R), and R-loops in the path of the fork which could have lethal consequences (RNA in red extruding from the RNA pol and base-paired to template DNA). Also, the block created by the R-loop in front of a replication fork will increase the supercoiling of the leading strand (−) behind the fork inducing a need for Top1 (green oval) to release the torsion. Top1 will produce multiple nicks at the ribonucleotides leading to genome instability. Nucleosome (represented by grey filled circles) assembly in the lagging strand could occur before OF maturation, leading to the incorporation of the RNA primer (represented in red) in nucleosomal DNA. The blue oval surrounding a nucleosome highlights this possibility.