FIG. 2.

Steady-state levels of UmuC (A) and UmuD (B) variants as determined by immunoblotting. (A) UmuC was expressed from the pGY9739 (umuDC) plasmids in all cases except UmuC(C105Y), which was expressed from pGY9738 (umuD′C). (B) In vivo cleavage efficiency of UmuD variants expressed from the pGY9739 plasmids. Cells were harvested 3 h after UV irradiation. (C) Purified wild-type UmuD and UmuD(G129S) were assayed for proficiency for cleavage in vitro with a RecA-ssDNA nucleoprotein filament, the presence of which is indicated by a plus sign and the absence of which is indicated by a minus sign. We did not detect cleavage of UmuD(G129S). Because of the low yield of purified UmuD(G129S), the results were detected by immunoblotting. WT, wild type; D, UmuD; C, UmuC.