Changes in gene expression in the Ras/adenylate cyclase system of Saccharomyces cerevisiae: correlation with cAMP levels and growth arrest.

Abstract

Levels of cyclic 3',5'-cyclic monophosphate (cAMP) play an important role in the decision to enter the mitotic cycle in the yeast, Saccharomyces cerevisiae. In addition to growth arrest at stationary phase, S. cerevisiae transiently arrest growth as they shift from fermentative to oxidative metabolism (the diauxic shift). Experiments examining the role of cAMP in growth arrest at the diauxic shift show the following: 1) yeast lower cAMP levels as they exhaust their glucose supply and shift to oxidative metabolism of ethanol, 2) a reduction in cAMP is essential for traversing the diauxic shift, 3) the decrease in adenylate cyclase activity is associated with a decrease in the expression of CYRi and CDC25, two positive regulators of cAMP levels and an increase in the expression of IRA1 and IRA2, two negative regulators of intracellular cAMP, 4) mutants carrying disruptions in IRAI and IRA2 were unable to arrest cell division at the diauxic shift and were unable to progress into the oxidative phase of growth. These results indicate that changes cAMP levels are important in regulation of growth arrest at the diauxic shift and that changes in gene expression plays a role in the regulation of the Ras/adenylate cyclase system.

SDC25, a dispensable Ras guanine nucleotide exchange factor of Saccharomyces cerevisiae differs from CDC25 by its regulation.

“…At the end of the growth phase, when glucose is exhausted, SDC25 mRNA started to be accumulated and later in stationary phase it reached a much higher level. In contrast, the CDC25 mRNA level was reduced when growth was arrested and remained low as already described (Russel et al, 1993). As an anabolic control, the level of TRP1 mRNA was drastically reduced in late stationary phase.…”

MOB1, an Essential Yeast Gene Required for Completion of Mitosis and Maintenance of Ploidy

“…However, the late nuclear division arrest has been characterized, to some extent, as the failure to complete a number of events. These events include the inactivation of the M phase-promoting protein kinase complex, Clb2p/Cdc28p, the disassembly of the mitotic spindle, the formation of prereplicative complexes on DNA origins, the lowering of cAMP levels, and the initiation of events responsible for cytokinesis (Smith et al, 1990;Russell et al, 1993;Spevak et al, 1993; Romanowski and Madine, 1996;Juang et al, 1997). These events may be regulated by the same or separate pathways that are triggered by a master switch at the end of anaphase.…”

Genetic Identification of Factors That Modulate Ribosomal DNA Transcription in Saccharomyces cerevisiae

“…One of the exceptions that did not cause an increase in rRNA signal in the qRT-PCR assay was ira1-Tn. Both IRA1 and IRA2, which were isolated from the screen multiple times, are required for proper entry into stationary phase (Russell et al 1993). Since the qRT-PCR assays were performed with cells growing in YPD media where rDNA transcription is active, it was possible that the ira1-Tn mutant and perhaps other FOA R mutants would have greater effects in the qRT-PCR assay in stationary phase where the rDNA is repressed.…”