Figure 4.

The spliced mRNP assembled in vitro targets mRNA for export. (A) Ftz pre-mRNA or Δi-mRNA was incubated under splicing conditions, and aliquots of these reactions were mixed with U6 snRNA and then injected into oocyte nuclei. Oocytes were incubated at 18°C for the indicated times and dissected, and total RNA was prepared from the nucleus (N) or cytoplasm (C). RNAs were analyzed on an 8% denaturing polyacrylamide gel. Breakdown products of the pre-mRNA or mRNA are indicated by the asterisks. Bands were quantitated by phosphorimager analysis, and the percent input mRNA exported was plotted (mRNA in cytoplasm/mRNA in the input lane). (B) Ftz pre-mRNA or Δi-mRNA was incubated under splicing conditions. Each reaction mixture then was fractionated on a Sephacryl-S 500 column. The positions of the spliced mRNP, Δi-mRNP, intron complex (i), and void volume (v) are indicated. (C) Same as A, except that the injected complexes first were partially purified by gel filtration (see B).