CONSERVATION OF FUNCTIONAL DOMAINS INVOLVED IN RNA-BINDING AND PROTEIN-PROTEIN INTERACTIONS IN HUMAN AND SACCHAROMYCES-CEREVISIAE PRE-MESSENGER-RNA SPLICING FACTOR SF1

The modular structure of splicing factor SF1 is conserved from yeast t o man and SF1 acts at early stages of spliceosome assembly in both org anisms, The hnRNP K homology (KH) domain of human (h) SF1 is the major determinant for RNA binding and is essential for the activity of hSF1 in spliceosome assembly, supporting the view that binding of SF1 to R NA is essential for its function, Sequences N-terminal to the KH domai n mediate the interaction between hSF1 and U2AF(65), which binds to th e polypyrimidine tract upstream of the 3' splice site, Moreover, yeast (y) SF1 interacts with Mud2p, the presumptive U2AF(65) homologue in y east, and the interaction domain is conserved in ySF1, The C-terminal degenerate RRMs in U2AF(65) and Mud2p mediate the association with hSF 1 and ySF1, respectively. Analysis of chimeric constructs of hSF1 and ySF indicates that the KH domain may serve a similar function in both systems, whereas sequences C-terminal to the KH domain are not exchang eable, Thus, these results argue for hSF1 and ySF1, as well as U2AF(65 ) and Mud2p, being functional homologues.