FIG. 1.

Mutant proteins do not cleave a plasmid substrate with bad coding flanks. (A) Plasmid substrate containing two good coding flanks was incubated with RAG proteins as indicated. The positions of the unrearranged substrate (UR), double-cut product (DC), single-cut (SC), and coding ends (CE) are indicated. A control incubation lacking RAG-1 protein was loaded in lane 4. (B) Plasmid substrate containing two bad coding flanks was assayed as in panel A. Asterisks indicate background bands generated by PvuII digestion at “star” sites (see Materials and Methods). The positions of substrate and cleavage products are as in panel A. Panels A and B show the same exposure of the same blot.