FIG. 4.

Roles of Rad6-Rad18-mediated ubiquitin conjugation and Ubc9-mediated SUMO attachment to the lysine 164 residue of PCNA. (A) In wild-type yeast cells, Rad6-Rad18-dependent processes play a predominant role in lesion bypass whereas Rad52-dependent recombinational bypass plays a relatively minor role. (B) Rad6-Rad18-dependent ubiquitin conjugation at the lysine 164 residue of PCNA promotes TLS by DNA Polζ and Polη and postreplicational repair of discontinuities that form in the newly synthesized DNA across from UV lesions. Ubc9-mediated SUMO modification of lysine 164 of PCNA is proposed to inhibit Rad52-dependent lesion bypass.