Genetic studies of the PWl7 gene of Saccharomyces cerevisiae: a domain essential for function maps to a nonconserved region of the protein

Abstract

The PRPl7 gene product is required for the second step of pre-mRNA splicing reactions. The G terminal half of this protein bears four repeat units with homology to the p transducin repeat. Missense mutations in three temperature-sensitive ppl7 mutants map to a region in the N-terminal half of the protein. We have generated, in vitro, 11 missense alleles at the p transducin repeat units and find that only one affects function in vivo. A phenotypically silent missense allele at the fourth repeat unit enhances the slow-growing phenotype conferred by an allele at the third repeastu, ggesting an interaction between these domains. Although many missense mutations in highly conserved amino acids lack phenotypic effects, deletion analysis suggests an essential role for these units. Only mutations in the N-terminal nonconserved domain of PRPl7 are synthetically lethal in combination with mutations in PRP16 and PRP18, two other gene products required for the second splicing reaction. A mutually allele-specific interaction between ppl7 and snr7, with mutations in U5 snRNA, was observed. We therefore suggest that the functional region of Prpl7p that interacts with Prpl8p, PrplGp, and U5 snRNA is in the N terminal region of the protein.