Mutations in cell division cycle genes CDC36 and CDC39 activate the Saccharomyces cerevisiae mating pheromone response pathway.

Abstract

Conditional mutations in the genes CDC36 and CDC39 cause arrest in the Gl phase of the Saccharomyces cerevisiae cell cycle at the restrictive temperature. We present evidence that this arrest is a consequence of a mutational activation of the mating pheromone response. cdc36 and cdc39 mutants expressed pheromoneinducible genes in the absence of pheromone and conjugated in the absence of a mating pheromone receptor.On the other hand, cells lacking the G. subunit or overproducing the Ga, subunit of the transducing G protein that couples the receptor to the pheromone response pathway prevented constitutive activation of the pathway in cdc36 and cdc39 mutants. These epistasis relationships imply that the CDC36 and CDC39 gene products act at the level of the transducing G protein. The CDC36 and CDC39 gene products have a role in cellular processes other than the mating pheromone response. A mating-type heterozygous diploid cell, homozygous for either the cdc36 or cdc39 mutation, does not exhibit the Gl arrest phenotype but arrests asynchronously with respect to the cell cycle. A similar asynchronous arrest was observed in cdc36 and cdc39 cells where the pheromone response pathway had been inactivated by mutations in the transducing G protein. Furthermore, cdc36 and cdc39 mutants, when grown on carbon catabolite-derepressing medium, did not arrest in Gl and did not induce pheromone-specific genes at the restrictive temperature.

Cell cycle arrest caused by CLN gene deficiency in Saccharomyces cerevisiae resembles START-I arrest and is independent of the mating-pheromone signalling pathway.

“…I assayed mating competence of a cln-[GAL-CLN3] strain after 4 h of incubation in glucose medium (as in Fig. 2 the requirement for receptor-pheromone interaction for mating (16,28,37,45). This is presumed to occur by constitutive activation of the pheromone response pathway, which includes START-I arrest (see the introduction).…”

“…Some mutations resulting in START-I arrest do so because the mutations are in genes that may be negative regulators of the pheromone response pathway; the mutations activate the pheromone response pathway in the absence of pheromone. cdc36, cdc39 (11,16,45,54,61), and scgl (17,28,37,43) mutations are in this category; only pheromone-responsive MATa or MATa cells are arrested at START by the mutations, while non-pheromone-responsive cells such as MATa/MATot diploids are not arrested at START. (Curiously, cdc36 and cdc39 mutations are still lethal in non-pheromone-responsive cells, but the lethality is not associated with specific cell cycle arrest.)…”

Model Systems For The Study Of Seven-Transmembrane-Segment Receptors

“…Like SST2 , however, the role of these components in regulating pheromone responsiveness is not yet known. The response mediated by these mutants requires functional 13-and y-subunits, and is suppressed by over expression of the a-SUbunit, suggesting that all three elements operate at the level of the G protein (162,163).…”

“…Temperature sensitive mutants of CD C36 and CDC39 will, at the restrictive temperature, constitutively activate the pheromone response pathway and promote mating (162,163). Like SST2 , however, the role of these components in regulating pheromone responsiveness is not yet known.…”

“…Recent evidence indicates that negative regulation of pheromone signaling also involves the CDC36 and CDC39 gene products (162,163). Temperature sensitive mutants of CD C36 and CDC39 will, at the restrictive temperature, constitutively activate the pheromone response pathway and promote mating (162,163).…”