FIGURE 7.

Ubc5AΔ138 supports allosteric cooperative activation of TRIM32. A, autoradiogram of the dependence of TRIM32-catalyzed polyubiquitin chain formation on the Ubc5AΔ138 concentration (lanes 5–14) in incubations containing 72 nm Uba1, 135 nm wild type Ubc5A, the indicated concentrations of Ubc5AΔ138, and 2.4 μm TRIM32 protein as indicated. The positions of the 5% stacking gel and free ¹²⁵I-ubiquitin are shown to the right. Migration positions for relative molecular weight standards are shown to the left. B, plot of the initial velocity for TRIM32-catalyzed ¹²⁵I-ubiquitin chain formation versus [Ubc5AΔ138]_o for the incubations in panel A as described under “Materials and Methods.”