FIG. 7.

The NRS purine-rich region and SR proteins promote U1 snRNP binding to the NRS. (A) Diagram of the constructs used in biotin-streptavidin affinity selection experiments. The larger and smaller shaded regions indicate the NRS purine-rich region and snRNP binding sites, respectively. (B) Affinity selection experiment. The indicated biotinylated RNAs (−, nonbiotinylated NRS RNA) were incubated in nuclear extract (NE; lanes 3 to 6), S100 (lanes 7 to 10), or S100 supplemented with SR proteins (lanes 11 to 14), and the complexes assembled on the RNA were affinity selected with streptavidin-agarose. Bound nucleic acids were released by treatment with proteinase K and phenol extracted, and RNA was electroblotted to a nylon membrane and hybridized with U1 and U11 antisense riboprobes. snRNA markers were extracted directly from nuclear extract or S100 (lanes 1 and 2). The positions of U1 and U11 are indicated to the right.