The yeast secretory pathway is perturbed by mutations in PMR1, a member of a Ca2+ ATPase family

The genes for two new P-type ATPases, PMR1 and PMR2, have been identified in yeast. A comparison of the deduced sequences of the PMR proteins with other known ion pumps showed that both proteins are very similar to Ca2+ ATPases. PMR1 is identical to SSC1, a gene previously identified by its effect on secretion of some foreign proteins from yeast. Proteins secreted from pmr1 mutants lack the outer chain glycosylation that normally results from passage through the Golgi. Loss of PMR1 function suppresses the lethality of ypt1-1, a mutation that blocks the secretion pathway. These data suggest that PMR1 functions as a Ca2+ pump affecting transit through the secretory pathway.

Mapping of functional domains within the Saccharomyces cerevisiae type 1 killer preprotoxin

Strains of Saccharomyces cerevisiae harboring M1-dsRNA, the determinant of type 1 killer and immunity phenotypes, secrete a dimeric 19-kd toxin that kills sensitive yeast cells by the production of cation-permeable pores in the cytoplasmic membrane. The preprotoxin, an intracellular precursor to toxin, has the domain sequence delta-alpha-gamma-beta where alpha and beta are the 9.5-and 9.0-kd subunits of secreted toxin. Plasmids containing a partial cDNA copy of M1, in which alpha, gamma, and beta are fused to the PH05 promoter and signal peptide, have previously been shown to express phosphate-repressible toxin production and immunity. Here the construction of a complete DNA copy of the preprotoxin gene and its mutagenesis are described. Analysis of the expression of these mutants from the PH05 promoter elucidates the functions of the preprotoxin domains. delta acts as a leader peptide and efficiently mediates the secretion, glycosylation and maturation of killer toxin. Mutations within the beta subunit indicate it to be essential for binding of toxin to and killing of whole cells but unnecessary for the killing of spheroplasts. Mutations within the putative active site of alpha prevent killing of both cells and spheroplasts. The probable role of beta is therefore recognition and binding to the cell wall receptor whereas alpha is the active ionophore. Mutations within alpha causing loss of toxicity also cause loss of immunity, while the mutants described within gamma and beta retain partial or complete immunity. Expression of gamma without alpha or beta confers no phenotype. The immunity determinant may minimally consist of the alpha domain and the N-terminal portion of gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of the positive-acting regulatory gene PHO4 from Saccharomyces cerevisiae

We have isolated a 10.2-kb fragment of yeast DNA from a genomic library of recombinant centromeric YCp50 plasmids, which complements a mutation in the PHO4 gene of Saccharomyces cerevisiae. The identity of the PHO4 gene on this plasmid was established by integration of a subfragment into the PHO4 region of the yeast chromosome. Analysis of a series of plasmid subclones covering different regions of the original yeast DNA insert localized the PHO4 gene within a 2.25-kb sequence. Southern hybridization of total genomic DNA prepared from wild-type strains and from integrative transformants show that the PHO4 gene consists of unique yeast DNA sequences and is present at a single copy in the S. cerevisiae genome. RNA blot hybridization mapping of transcripts within this genomic region identify the PHO4 transcript as a 1.7-kb, low-abundancy, constitutively expressed and polyadenylated RNA.