FIG. 3.
Time course studies of protein-RNA complex formation on the WT Sp/PA substrate and a nonspecific RNA substrate containing no processing elements. The complexes noted are a nonspecific complex (N), which forms rapidly on either substrate, and three specific complexes (AC, AC′, and BC), which form only on the WT Sp/PA complex. The subscript C (for “coupled”) is used to denote these complexes as forming on a coupled Sp/PA substrate and to differentiate them from spliceosomal complexes, which form on splicing-only substrates.