FIG. 3.

Pre-mRNA and the lariat-intron intermediate coprecipitate with Snu17p under in vitro splicing conditions. Splicing reactions using either extracts containing Snu17p without tag (lanes 1 to 3 and 7 to 9) or protein-A tagged Snu17p (lanes 4 to 6 and 10 to 12) were incubated under splicing conditions with ³²P-labeled actin pre-mRNA (lanes 1 to 6) or U3 pre-mRNA (lanes 7 to 12) for 20 or 40 min at 25°C. Then 93% of the 40-min reaction volume was precipitated with IgG agarose. For each time point, 7% of the total reaction mixtures (lanes 1, 2, 4, 5, 7, 8, 10, and 11) and the precipitate from the remaining 93% of the reaction mixtures (IP; lanes 3, 6, 9 and 12) were assayed for the presence of pre-mRNA, splicing intermediates, and products. Indicated on the left and on the right are the identities of the labeled RNA species: intron-lariat-exon 2 intermediate, excised lariat-intron, pre-mRNA, mature mRNA, and cleaved exon 1 intermediate.