FIG. 5.

EMSA of wild-type PRE fragment III binding to GST-PTB and competition by oligoribonucleotides. ³²P-labeled PRE fragment III was incubated with or without (lanes 2 and 1, respectively) 8 ng of GST-PTB and electrophoresed on a native polyacrylamide gel. In addition, unlabeled oligoribonucleotides corresponding to a known PTB site (P3) from intron 2 of α-tropomyosin (lanes 3 and 4) (31), site 2 of fragment III (lanes 5 and 6), mutant site 2 (lanes 7 and 8), and site 1 of fragment III (lanes 9 and 10) were included in the incubation mixture at a 50 or 100-fold molar excess (even- and odd-numbered lanes, respectively) over the amount of labeled probe.