SPECIFIC PROTEIN-PROTEIN INTERACTIONS BETWEEN THE ESSENTIAL MAMMALIANSPLICEOSOME-ASSOCIATED PROTEINS SAP-61 AND SAP-114

Spliceosome-associated proteins (SAPs) 61, 62, and 114 can be UV-cross linked to pre-mRNA in purified spliceosomal complexes and are associat ed with U2 small nuclear ribonucleoproteins (snRNP). These proteins al so compose the essential heterotrimeric splicing factor SF3a, and prod ucts of yeast pre-mRNA processing genes PRP9, PRP11, and PRP21 are the ir likely yeast counterparts. We report the isolation of a cDNA encodi ng SAP 61 and find that it is 30% identical in amino acid sequence to PRP9. A C-terminal Cys(2)His(2) zinc-finger-like motif, which could be involved in the pre-mRNA binding, is the most highly conserved region of the protein. We also demonstrate specific protein-protein interact ions between SAPs 61 and 114 and show that the N terminus of SAP 61 is required for this interaction. Significantly, the corresponding prote ins are also known to interact in yeast: PRP9 interacts with PRP21, an d the N-terminal portion of PRP9 is required. Previous work showed tha t direct interactions also occur between SAPs 62 and 114 and between t he corresponding PRPs 11 and 21. These observations indicate that the specific protein-protein interactions that occur between the three pre spliceosomal factors have been conserved between yeast and mammals.