INTERACTION OF MAMMALIAN SPLICING FACTOR SF3A WITH U2 SNRNP AND RELATION OF ITS 60-KD SUBUNIT TO YEAST PRP9

In the assembly of a prespliceosome, U2 small nuclear ribonucleoprotei n (snRNP) functions in pre-messenger RNA (mRNA) splicing together with splicing factors (SFs) 3a, SF3b, and several other proteins. The 17S but not the 12S form of U2 snRNP is active in splicing-complex formati on. Here it is shown that the SF3a subunits correspond to three of the 17S U2 snRNP-specific polypeptides. SF3a interacts with U2 snRNP in t he presence of SF3b to generate a structure similar to 17S U2 snRNP, w hich suggests a function for SF3a and SF3b in the incorporation of U2 snRNP into the spliceosome. Furthermore, the 60-kilodalton subunit of SF3a is related to the yeast splicing protein PRP9.