Oncogene Homologs

Transcription of the mat1-Pm gene of Schizosaccharomyces pombe controlling entry into meiosis is stimulated by the mating pheromone, M-factor. We have studied its expression by monitoring beta-galactosidase activity in cells carrying a plasmid-borne mat1-Pm/lacZ fusion construct. Stimulation required the M-factor receptor (Map3) and other proteins (Gpa1, Byr1, Byr2 and Spk1) thought to be involved in propagating the pheromone signal within the cell. Mutational activation of gpa1 encoding an alpha subunit of the receptor-coupled heterotrimeric G protein causes full expression of mat1-Pm even in the absence of pheromone, suggesting that Gpa1 is a key signal transmitter. Furthermore, an activated ras1val17 mutant exhibited a much stronger level of induction than wild-type cells, though full expression needs M-factor treatment. Deletion analysis of the mat1-Pm promoter region identified a stretch of 21 bp that is shown to play a critical role in controlling expression. This region lies just upstream of a TATA-like box and contains a TR-box (TTCTTTGTTY) motif which is the recognition site of a putative transcription factor Ste11. Point mutations in the TR-box motif abolished the expression of mat1-Pm/lacZ. Almost no expression of mat1-Pm was detected in a ste11 deletion mutant, whereas overproduction of Ste11 greatly increased the expression.

Mating pheromone‐induced expression of the MAT1‐Pm gene of Schizosaccharomyces pombe: Identification of signalling components and characterization of upstream controlling elements

Aono

Yanai

Miki

et al. 1994

Molecular cloning of the plc1⁺ gene of Schizosaccharomyces pombe, which encodes a putative phosphoinositide‐specific phospholipase C

Andoh

Yoko-o

Matsui

et al. 1995

Exploiting the polymerase chain reaction, we have isolated a gene that encodes a putative phosphoinositide-specific phospholipase C (PLC) of the fission yeast Schizosaccharomyces pombe. Inspection of the nucleotide sequence of the gene revealed an open reading frame that can encode a polypeptide of 899 amino acid residues with a calculated molecular mass of 102 kDa. This putative polypeptide contains both the X and Y regions that are conserved among three classes of mammalian PLC, and also contains a presumptive Ca(2+)-binding site (an E-F hand motif). The structure of the putative protein is most similar to that of the delta class of PLC isozymes. To investigate the role of this gene, designated plc1+, gene disruption was carried out by interrupting the coding region with the ura4+ marker. Growth of plc1 cells was temperature-sensitive in rich medium, and cells could not grow in synthetic medium. Expression of the PLC1 gene of Saccharomyces cerevisiae suppressed the growth defect phenotype of plc1- cells, a strong suggestion that the plc1+ gene encodes PLC.

Biochemical similarity of Schizosaccharomyces pombe ras1 protein with RAS2 protein of Saccharomyces cerevisiae

Onozawa

Danjoh

Fujiyama

1995

The mechanism by which yeast rus2 mutant hyperaccumulates glycogen has been investigated. Total glycogen synthase activity WHS between 2.5 and 1.3 times higher in the rus2 mutant than in an isogenic strain. In addition, while in the normal strain the glycogen synthase activation state decreased along the exponential phase, in the mutant strain the opposite behaviour was observed: glycogen synthase activation state rose continuously reaching full activation at the beginning of the stationary phase. Glycogen phosphorylase a activity was up to 40 times higher in the mutant than in the normal strain. Glucose 6-phospha'te and fructose 2,G-bisphosphate levels were slightly more elevated in the mutants. The increase in total glycogen synthase and, particularly, the full activation of this enzyme may explain glycogen hyperaccumulation in the rus2 mutant even in the presence of elevated levels of glycogen phosphorylase a.