e G-protein-coupled receptors (GPCRs) are integral membrane proteins that initiate responses to extracellular stimuli by mediating ligand-dependent activation of cognate heterotrimeric G proteins. In yeast, occupancy of GPCR Ste2 by peptide pheromone ␣-factor initiates signaling by releasing a stimulatory G␤␥ complex (Ste4-Ste18) from its inhibitory G␣ subunit (Gpa1). Prolonged pathway stimulation is detrimental, and feedback mechanisms have evolved that act at the receptor level to limit the duration of signaling and stimulate recovery from pheromone-induced G 1 arrest, including upregulation of the expression of an ␣-factor-degrading protease (Bar1), a regulator of G-protein signaling protein (Sst2) that stimulates Gpa1-GTP hydrolysis, and Gpa1 itself. Ste2 is also downregulated by endocytosis, both constitutive and ligand induced. Ste2 internalization requires its phosphorylation and subsequent ubiquitinylation by membrane-localized protein kinases (Yck1 and Yck2) and a ubiquitin ligase (Rsp5). Here, we demonstrate that three different members of the ␣-arrestin family (Ldb19/Art1, Rod1/Art4, and Rog3/ Art7) contribute to Ste2 desensitization and internalization, and they do so by discrete mechanisms. We provide genetic and biochemical evidence that Ldb19 and Rod1 recruit Rsp5 to Ste2 via PPXY motifs in their C-terminal regions; in contrast, the arrestin fold domain at the N terminus of Rog3 is sufficient to promote adaptation. Finally, we show that Rod1 function requires calcineurin-dependent dephosphorylation.

Much like mammalian cells, yeast contain a Rho-dependent pathway for endocytosis in addition to canonical clathrin-dependent endocytosis.

Background: During energy starvation, cells utilize intracellular resources for survival; however, the resources used during glucose starvation are unknown. Results: In glucose-starved yeast, vacuolar hydrolysis and endocytosis promote survival whereas autophagy is dispensable. Conclusion: Vacuolar hydrolysis blocks autophagy and provides resources for survival during glucose starvation. Significance: This new survival mechanism could protect cells from starvation in many situations.

No abstract

Rab is a family of small Ras-like GTPases regulating intracellular vesicle transport. We have previously reported that prenylated Rab acceptor or PRA1 interacts with Rab GTPases and vesicle-associated membrane protein (VAMP2). Structural prediction programs suggest that PRA1, with its two extensive hydrophobic domains, is likely to be an integral membrane protein. However, subcellular fractionation and immunocytochemical analyses indicated that PRA1 is localized both in the cytosol and tightly associated with the membrane compartment. The membrane-bound form can be partially extracted with physiological buffer and urea, suggesting that PRA1 is an extrinsic membrane protein.Deletion of the carboxyl-terminal domain resulted in a protein that behaved as an integral membrane protein, indicating that this domain plays an essential role in maintaining PRA1 in a soluble state. PRA1 can also bind weakly to GDP dissociation inhibitor (GDI), a protein involved in the solubilization of membrane-bound Rab GTPases. Addition of PRA1 inhibited the extraction of membrane-bound Rab3A by GDI, suggesting that membrane localization of Rab GTPases is dependent on the opposing action of PRA1 and GDI. The binding of Rab and VAMP2 to PRA1 is mutually exclusive such that Rab3A can displace VAMP2 in a preformed VAMP2-PRA1 complex.