Fig. 4.

2D gel electrophoresis of partially purified human spliceosomal A complexes. Spliceosomal complexes were allowed to form on MINX pre-mRNA and then purified via MS2 affinity selection. Proteins were separated by 2D gel electrophoresis using the conditions for the analysis of high-molecular-mass proteins (see Fig. 8A for analysis of spliceosomal proteins with molecular masses less than 25 kDa) and then stained with Sypro Ruby (A) or with Pro-Q Diamond (B). Spots were visualized by fluoroimaging. All spots visible after silver staining were analyzed by mass spectrometry, and the identified proteins are indicated by a number (see Table 1 for the identities of the numbered spots). MS2-MBP (present in ∼6 copies per complex) is labeled. Spots containing proteolytic fragments are indicated by an asterisk, those not identified are indicated by “N,” and those corresponding to RNases are indicated by “R.”