Labeled DNA fragments containing wild-type sites A and B bound to zinc-finger domains of BLMP-1 expressed in E. coli). However, labeled DNA fragment with mutated A and B sites failed to bind. Moreover, this binding could be competed by excess unlabeled wild-type DNA, but not by DNA fragments in which A and B sites were mutated either individually or together. This demonstrates that both A and B sites are required for binding to the BLMP-1 protein. Since mutating the same sites abolishes enhancer activity, authors conclude that BLMP-1 directly binds to these sites and positively regulates
bed-3 transcription.