A proposed working model for the budding yeast PRR pathways.

MRX, in conjunction with Sae2, functions upstream of PCNA monoubiquitination by ssDNA resection thus promoting Rad6-Rad18 to monoubiquitinate PCNA. Exo1 processes ssDNA gaps in the 5′-3′ direction, which facilitates PCNA polyubiquitination by Rad5-Ubc13-Mms2 and subsequent error-free lesion bypass mediated by the Shu complex, HR and Sgs1-Top3 resolution.

MRX与Sae2协同作用，通过单链DNA（single-stranded DNA, ssDNA）末端切除参与增殖细胞核抗原（Proliferating Cell Nuclear Antigen, PCNA）单泛素化的上游调控过程，进而促进Rad6-Rad18复合物对PCNA的单泛素化修饰。核酸外切酶1（Exonuclease 1, Exo1）以5′→3′方向加工单链DNA间隙，该过程可促进Rad5-Ubc13-Mms2复合物介导的PCNA多泛素化，以及后续由Shu复合物、同源重组（Homologous Recombination, HR）和Sgs1-Top3复合物解离过程所介导的无错损伤旁路修复途径。