Identification and characterization of yUAP/Sub2p, a yeast homolog of the essential human pre-mRNA splicing factor hUAP56.

The human 56-kD U2AF(65)-associated protein (hUAP56), a member of the DExD/H box protein family of RNA-dependent ATPases, is required for the stable binding of U2 snRNP to the pre-mRNA branchpoint. Here we identify a highly conserved Saccharomyces cerevisiae homolog of hUAP56, yUAP/Sub2p. yUAP/Sub2p can be functionally substituted for by hUAP56 and, like its human counterpart, is an essential pre-mRNA splicing factor. yUAP/Sub2p is required for formation of the commitment complex, the precursor for U2 snRNP addition. In conjunction with previous studies, we conclude that at least two DExD/H box proteins, Prp5p and yUAP/Sub2p, mediate the U2 snRNP-branchpoint interaction.