Multiple forms of PU.I bind to the intron of the EDN gene. (A) DNA affinity precipitation of nuclear extracts from HL60 (H), HL60 7.7 (7), or BA-treated HL60 7.7 cells (B). Either wild-type (lanes 1 through 3) or mutant PU.I oligonucleotide (lanes 4 through 6) was used as a probe. Proteins bound to these probes were precipitated, separated through a 12% polyacrylamide gel, and blotted onto nylon membranes. The filter was then probed with an anti-PU.I antibody. Three different forms of PU.I bind to the wild-type PU.I probe, of which only the largest form binds (with lower affinity) to the mutant probe. (B) Immunoprecipitation of PU.I from HL60 (H), HL60 7.7 (7), or BA-treated HL60 7.7 cells (B) using an anti-PU.I antibody. The precipitates were visualized as in (A). The same three PU.I forms are detected as in (A).