FIG. 6.

The N-terminal regions and the zinc finger domains of SF3a60 and SF3a66 are essential for prespliceosome formation. The assembly of presplicing complex A was tested in the presence of buffer (−), HeLa cell nuclear extract (NE), or fractions containing partially purified SF1, U1 snRNP, the 12S U2 snRNP, U2AF, and SF3b. HeLa cell SF3a or recombinant proteins were added as indicated. Splicing complexes were separated in a native 4% polyacrylamide gel. The positions of pre-mRNA, complex H, presplicing complex A, and splicing complexes B and C are indicated on the left.