The ras-like yeast YPT1 gene is itself essential for growth, sporulation, and starvation response.

Abstract

The Saccharomyces cerevisiae gene YPTI encodes a protein that exhibits significant homology to the mammalian ras proteins. Using gene disruption techniques, we have shown that the intact YPTI gene is required for spore viability. Lethality caused by loss of YPTI function, unlike that caused by loss of the yeast ras homologs RAS] and RAS2 function, is not suppressed by the bcyl mutation, suggesting that YPTI does not act through the adenylate cyclase regulatory system. A cold-sensitive allele, yptl-1, was constructed. At the nonpermissive temperature, mutants died, exhibiting aberrant nuclear morphology, as well as abnormal distribution of actin and tubulin. The mutant cells died without exhibiting classical cell-cycle-specific arrest; nevertheless, examination of cellular DNA content suggests that the YPTI function is required, particularly after S phase. Cells carrying the yptl-l mutation died upon nitrogen starvation even at a temperature permissive for growth; diploid cells homozygous for yptl-l did not sporulate. The YPTI gene is thus involved in nutritional regulation of the cell cycle as well as in normal progression through the mitotic ceDl cycle.

Regulation of selective autophagy onset by a Ypt/Rab GTPase module

“…In both assays, under nitrogen starvation trs85Δ confers a more severe phenotype than atg11Δ. These results are in agreement with the idea that Ypt1 and Trs85 play a role in both selective and nonselective autophagy (15,17). The observation that atg11Δ mutant cells also exhibit mild growth and Pho860 defects under nitrogen starvation is in agreement with the idea that the PAS assembled during normal growth can persist and help cells survive under starvation conditions (29).…”

“…Cells carrying the ypt1-1 mutation, T40K, in the effector-binding domain of Ypt1 are defective in autophagy (15,17). Therefore, we tested whether the Ypt1-1 mutant protein is defective in the interaction with Atg11 using the three interaction assays mentioned above: yeast-two hybrid, coprecipitation with Atg11-HA from yeast lysates and coprecipitation with bacterially expressed His-Atg11-CC2-3 ( Fig.…”

“…Ypt1 and its mammalian homolog Rab1 play a role in autophagy (15,16), and Trs85, in the context of the TRAPP III complex, can act as a Ypt1 GEF in this process (17). However, the molecular mechanism by which Ypt1 and Rab1 regulate autophagy is unknown, and it is not clear whether it is dependent on their well-documented function in ER-toGolgi transport.…”

Yeast actin cytoskeleton mutants accumulate a new class of Golgi-derived secretary vesicle.

“…No anti-a-1,6-mannose labeling was observed on the nuclear or peripheral ER in either mutant or wild-type cell sections. These results suggest that the vesicles that accumulate in these mutants are, in fact, Golgi-derived. Yptlp, like Sec4p, is a small GTPase; the sequences of the two proteins are highly homologous and their function is largely preserved in chimeras made between them (Schmitt et al, 1986;Segev and Botstein, 1987;Schmitt et al, 1988;Segev et al, 1988;Dunn et al, 1993). However, unlike Sec4p, Yptlp is required for vesicular transport early in the secretory pathway, between the ER and the Golgi (Segev et al, 1988;Bacon et al, 1989).…”

Identification of ras-related, YPT family genes in Schizosaccharomyces pombe.

“…cerevisiae YPTI has been reported to be involved in microtubule organization (Schmitt et al, 1986), in regulation of intracellular calcium (Schmitt et al, 1988) and in sporulation and starvation response (Segev and Botstein, 1987). Its primary function may be in the transportation of secretory vesicles (Segev et al, 1988), which apparently is the case with S. cerevisiae SEC4 (Salminen and Novick, 1987).…”