Functional conservation of the human homolog of the yeast pre-mRNA splicing factor Prp17p

Splicing of pre-mRNAs involves two sequential transesterification reactions commonly referred to as the first and second steps. In Saccharomyces cerev isiae, four proteins, Prp16p, Prp17p, Prp18p, and Slu7p are exclusively req uired for the second step of splicing. The human homologs of Prp16p, Prp17p , and Prp18p have been identified, and the human proteins hPrp16 and hPrp18 have been shown to be required for the second step of splicing in vitro. H ere we provide further evidence for the functional conservation of the seco nd step factors between yeast and humans. Human hPrp17, which is 35% identi cal to the S. cerevisiae protein, is able to partially rescue the temperatu re sensitive phenotype in a yeast strain where PRP17 has been knocked out, suggesting that the human and yeast proteins are functionally conserved. Ov erexpression of hPrp17 in the knockout yeast strain partially rescues the s plicing defect seen in vitro and in vivo. In HeLa cells, hPrp17 is highly c oncentrated in the nuclear speckles, as is SC35 and many other splicing fac tors, thus providing further support that this protein also functions as a splicing factor in humans.