FIG. 2.

Mapping the interaction sites in histone pre-mRNA. (A) Sequences of biotinylated RNA halves. The U7-binding site is underlined, and nucleotide substitutions within the purine core of the mutant DCP RNA are indicated with lowercase letters. (B) Western blot analysis of affinity-purified complexes assembled on 5′ biotinylated RNAs (12.5 pmol), as indicated at the top of each lane. Processing complexes were formed in the presence of 0.2% NP-40 by using RNA substrates shown in panel A and subsequently purified on streptavidin beads. The presence of individual proteins bound to each RNA was detected by specific antibodies. In the top panel, anti-mouse 3′hExo and anti-SLBP antibodies were mixed. Lane 1 contains 10% of the extract used to assemble processing complexes on each RNA species.