FIGURE 2.

Different E2 enzymes could only utilize distinct subsets of the single lysine/arginine derivatives of ubiquitin to produce ubiquitin conjugates. Each E2 enzyme was incubated in a reaction mixture containing the indicated single lysine/arginine ubiquitin derivative. Formation of ubiquitin conjugates was estimated by Western blot analysis with anti-ubiquitin antibody. Representative analyses of such lysine specificity determinations for E2C (A) and E2S (B) are presented. IB, immunoblot.