Pre-mRNA splicing in Schizosaccharomyces pombe: regulatory role of a kinase conserved from fission yeast to mammals.

Most primary messenger RNA transcripts (pre-mRNAs) in eukaryotes contain intervening sequences that must be precisely removed to generate a functional mRNA. The excision of the intervening sequences, the introns, from a pre-mRNA and the concomitant joining of the flanking sequences, the exons, is called pre-mRNA splicing. Pre-mRNA splicing takes place in large ribonucleoprotein machinery, the spliceosome. Although the function and components of this machinery appear to be highly conserved between organisms, many distinct differences between budding yeast, Saccharomyces cerevisiae, and fission yeast, Schizosaccharomyces pombe, have been found, emphasizing their evolutionary distance. Most interestingly, fission yeast appears to reflect the more conservative evolutionary development regarding pre-mRNA splicing. Many spliceosomal components, including the five small nuclear RNAs, which most likely form the catalytic core of the spliceosome, show a higher degree of similarity with the components of the splicing machinery found in mammals. In addition, several regulatory components of the spliceosome detected in mammals are absent in Sac. cerevisiae, but present in Sch. pombe. Here, we review recent progress made in our understanding of the control of pre-mRNA splicing in Sch. pombe. The focus is on Prp4p kinase, first discovered in fission yeast and also present in mammals, but absent in Sac. cerevisiae. Results from both mammals and Sch. pombe suggest that Prp4p plays a key role in regulating pre-mRNA splicing and in connecting this process with the cell cycle.