Fig. 3. Ability of UNG and R276X mutant proteins to bind Ugi.

Reaction mixtures (15 µl) containing 40 pmol of E. coli Ung (lanes 2 and 3), UNG (lanes 4 and 5), or R276X mutant protein (lanes 6–41), with or without (+ or −) Ugi (100 pmol) were incubated as described under “Experimental Procedures.” A control reaction containing Ugi (100 pmol) alone was similarly processed (lane 1). Samples were analyzed at 4 °C by non-denaturing 10% polyacrylamide gel electrophoresis, proteins were visualized with Coomassie Brilliant Blue G-250 stain, and the gel was imaged as described under “Experimental Procedures.” Arrows indicate the location of Ung, UNG, Ugi, Ung·Ugi, UNG·Ugi, and the tracking dye front (TD). Arg²⁷⁶ mutant protein lane assignments are indicated by single letter amino acid abbreviations.