The Prp5 protein (Prp5p) is a putative RNA helicase required for
pre-spliceosome formation in the pre-mRNA splicing pathway in
Saccharomyces cerevisiae . To identify additional factors involved
in this step, we isolated extragenic suppressors of the ts prp5-1
mutation. One of these, spp51-1 , is also recessive and cs.
Suppression by spp51-1 is allele- and gene-specific. Northern
blot analyses show that spp51-1 suppresses the splicing defect of
prp5-1 . At temperatures below optimal, spp51-1 alone
confers a mild splicing defect in vivo. Furthermore, spp51-1
mutant extracts in vitro have reduced splicing efficiencies at 15
degrees. Finally, spp51-1 is synthetically lethal with the
prp9 and prp21 mutations which confer defects in pre-spliceosome formation. The wildtype SPP51 gene was cloned by
complementation and was found to be RPB5 . Rpb5p is one of five
subunits common to all three RNA polymerases, and is conserved from
archaea to humans. Rpb5p is essential but its function in transcription
is unknown (Woychik et al. (1990). Genes Dev. 4:313). Our genetic data
suggest that PRP5 and RBP5 act in the same pathway and
that their protein products interact physically or functionally. The two
proteins could physically interact if the transcriptional and
spliceosomal complexes associate or if Rpb5p is a subunit of the
spliceosome. We are currently determining by biochemical assays if Rpb5p
and Prp5p physically associate.
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