Deletion of MUD2, the yeast homolog of U2AF65, can bypass the requirement for Sub2, an essential spliceosomal ATPase

Mammalian U2AF65 and UAP56 are required for prespliceosome (PS) formation. We tested the predictions that the yeast UAP56 homolog, SUBS is required fo r the same step and functions collaboratively with MUDS the yeast homolog o f U2AF65. Unexpectedly, sub2-1. extracts accumulate PS-like complexes. More over, deletion of MUD2 exacerbates the cs phenotype of sub2 alleles yet sup presses both the is sub2-1 and the lethal Delta sub2 phenotypes. We propose that Sub2 functionally interacts with Mud2 both before and after PS format ion. In the absence of Mud2, Sub2 function becomes dispensable.