Sequence elements that contribute to the degradation of yeast G alpha.
BACKGROUND
Gpa1 is the alpha subunit of the yeast G-protein that regulates signal transduction during mating. The stability of Galpha/Gpa1 is influenced by the ubiquitin-dependent N-end rule pathway, suggesting that the regulation of G alpha levels may be important for effective mating response and recovery.


RESULTS
The G alpha sequences that confer sensitivity to degradation by the N-end rule pathway were identified. The insertion of this degradation signal (G1-Deg) into the ordinarily stable Gpa2 protein conferred proteolytic targeting. We examined G alpha degradation under different conditions and found that it was efficiently degraded in haploid and diploid cells, but was stable if it was synthesized prior to expression of the N-end rule pathway. Interestingly, a specific mutation in G alpha that is believed to promote the GTP-bound form (N388K) caused accelerated degradation.


CONCLUSIONS
A region encompassing a putative effector-binding domain (G1-Deg) is required for G alpha degradation via the N-end rule pathway. Our studies have shown that G alpha is susceptible to proteolysis soon after synthesis. These results are in agreement with the idea that G alpha is more unstable in the GTP-bound form, which is the predominant state of monomeric/free G alpha soon after synthesis. It is likely that the signal transduced by Gbetagamma can be regulated by adjusting the levels of G alpha through proteolysis.
Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway 08854, USA.
C
C
Schauber
L
L
Chen
P
P
Tongaonkar
I
I
Vega
K
K
Madura
D000595:Amino Acid Sequence; D004171:Diploidy; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006238:Haploidy; D020962:Heterotrimeric GTP-Binding Proteins; D010447:Peptide Hydrolases / Q000378:metabolism*; D010675:Pheromones; D014176:Protein Biosynthesis; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D015398:Signal Transduction; D013379:Substrate Specificity; D013997:Time Factors; D014452:Ubiquitins / Q000378:metabolism*; D020710:RGS Proteins
D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins; D020690:GTPase-Activating Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D010447:Peptide Hydrolases; D010675:Pheromones; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; C094301:SST2 protein, S cerevisiae; D020710:RGS Proteins; C084293:GPA1 protein, S cerevisiae