The N-terminus of Prp1 (Prp6/U5-102 K) is essential for spliceosome activation in vivo.

The spliceosomal protein Prp1 (Prp6/U5-102 K) is necessary for the integrity of pre-catalytic spliceosomal complexes. We have identified a novel regulatory function for Prp1. Expression of mutations in the N-terminus of Prp1 leads to the accumulation of pre-catalytic spliceosomal complexes containing the five snRNAs U1, U2, U5 and U4/U6 and pre-mRNAs.

Fission yeast Prp4p kinase regulates pre-mRNA splicing by phosphorylating a non-SR-splicing factor.

We provide evidence that Prp4p kinase activity is required for pre-mRNA splicing in vivo and show that loss of activity impairs G1-S and G2-M progression in the cell cycle. Prp4p interacts genetically with the non-SR (serine/arginine) splicing factors Prp1p and Prp5p. Bacterially produced Prp1p is phosphorylated by Prp4p in vitro.