Yeast mitochondrial transcript and gene product abundance has been observed to increase upon release from glucose repression, but the mechanism of regulation of this process has not been determined. We report a kinetic analysis of this phenomenon, which demonstrates that the abundance of all classes of mitochondrial RNA changes slowly relative to changes observed for glucose-repressed nuclear genes. Several cell doublings are required to achieve the 2-to 20-fold-higher steady-state levels observed after a shift to a nonrepressing carbon source. Although we observed that in some yeast strains the mitochondrial DNA copy number also increases upon derepression, this does not seem to play the major role in increased RNA abundance. Instead we found that three-to sevenfold increases in RNA synthesis rates, measured by in vivo pulse-labelling experiments, do correlate with increased transcript abundance. We found that mutations in the SNF1 and REG] genes, which are known to affect the expression of many nuclear genes subject to glucose repression, affect derepression of mitochondrial transcript abundance. These genes do not appear to regulate mitochondrial transcript levels via regulation of the nuclear genes RP041 and MTF1, which encode the subunits of the mitochondrial RNA polymerase. We conclude that a nuclear gene-controlled factor(s) in addition to the two RNA polymerase subunits must be involved in glucose repression of mitochondrial transcript abundance.Mitochondria are the site of many complex biochemical processes, including the citric acid cycle, oxidative phosphorylation, and electron transport (reviewed in reference 1). In addition to these processes, the organelles maintain their own genomes and transcribe and synthesize the proteins they encode (reviewed in references 7 and 33). In addition to being dependent on the organelle-encoded gene products, mitochondria are functionally dependent upon many genes encoded in the nuclear genome for all of these processes. Mitochondrial activity in the yeast Saccharomyces cerevisiae is subject to regulation; under repressing conditions, such as anaerobic growth or growth on glucose, mitochondrial activity is minimal. However, under derepressing conditions, such as growth on a nonfermentable carbon source, mitochondrial activity is high and the requirement for mitochondrial enzymes increases (7,26). Since expression of the mitochondrial genes is dependent on nuclear genes, coordinated regulation of expression of the nuclear and mitochondrial genomes must be involved in these changes.It is well documented that glucose repression is a major regulatory system in yeast cells and affects a large number of nuclear genes and gene products (reviewed in references 35 and 36). It has also been shown that glucose repression affects the mitochondrion in several ways. The expression of many nucleus-encoded mitochondrial genes is glucose repressed at the levels of transcription and RNA stability (reviewed in references 20, 35, and 36). pressed cells (reviewed in references 7 and 33)...

The angiotensin II type I (AT 1 ) receptor mediates regulation of blood pressure and water-electrolyte balance by Ang II. Substitution of Gly for Asn 111 of the AT 1 receptor constitutively activates the receptor leading to Gq-coupled IP 3 production independent of Ang II binding. The Ang II-activated conformation of the AT1 N111G receptor was proposed to be similar to that of the wild-type AT 1 receptor, although, various aspects of the Ang II-induced conformation of this constitutively active mutant receptor have not been systematically studied. Here, we provide evidence that the conformation of the active state of the wild-type and the constitutively active AT 1 receptors are different. Upon Ang II binding an activated conformation of the wild-type AT 1 receptor activates G protein and recruits barrestin. In contrast, the agonist-bound AT1 N111G mutant receptor preferentially couples to Gq and is inadequate in b-arrestin recruitment.

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Yeast mitochondrial transcript and gene product abundance has been observed to increase upon release from glucose repression, but the mechanism of regulation of this process has not been determined. We report a kinetic analysis of this phenomenon, which demonstrates that the abundance of all classes of mitochondrial RNA changes slowly relative to changes observed for glucose-repressed nuclear genes. Several cell doublings are required to achieve the 2- to 20-fold-higher steady-state levels observed after a shift to a nonrepressing carbon source. Although we observed that in some yeast strains the mitochondrial DNA copy number also increases upon derepression, this does not seem to play the major role in increased RNA abundance. Instead we found that three- to sevenfold increases in RNA synthesis rates, measured by in vivo pulse-labelling experiments, do correlate with increased transcript abundance. We found that mutations in the SNF1 and REG1 genes, which are known to affect the expression of many nuclear genes subject to glucose repression, affect derepression of mitochondrial transcript abundance. These genes do not appear to regulate mitochondrial transcript levels via regulation of the nuclear genes RPO41 and MTF1, which encode the subunits of the mitochondrial RNA polymerase. We conclude that a nuclear gene-controlled factor(s) in addition to the two RNA polymerase subunits must be involved in glucose repression of mitochondrial transcript abundance.

β-Arrestins turn off G protein-mediated signals and initiate distinct G protein-independent signaling pathways. We previously demonstrated that angiotensin AT1 receptor-bound β-arrestin 1 is cleaved after Phe388 upon angiotensin II stimulation. The mechanism and signaling pathway of angiotensin II-induced β-arrestin cleavage remain largely unknown. Here, we show that protein Tyr phosphatase activity is involved in the regulation of β-arrestin 1 cleavage. Tagging of green fluorescent protein (GFP) either to the N-terminus or C-terminus of β-arrestin 1 induced conformational changes and the cleavage of β-arrestin 1 without angiotensin AT1 receptor activation. Orthovanadate and molybdate, inhibitors of protein Tyr phosphatase, attenuated the cleavage of C-terminal GFP-tagged β-arrestin 1 in vitro. The inhibitory effects of okadaic acid and pyrophosphate, which are inhibitors of protein Ser/Thr phosphatase, were less than those of protein Tyr phosphatase inhibitors. Cell-permeable pervanadate inhibited angiotensin II-induced cleavage of β-arrestin 1 in COS-1 cells. Our findings suggest that Tyr phosphorylation signaling is involved in the regulation of angiotensin II-induced β-arrestin cleavage.