Sequence elements that contribute to the degradation of yeast Gα

Background Gpa1 is the α subunit of the yeast G‐protein that regulates signal transduction during mating. The stability of Gα/Gpa1 is influenced by the ubiquitin‐dependent N‐end rule pathway, suggesting that the regulation of Gα levels may be important for effective mating response and recovery. Results The Gα 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 Gα 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 Gα that is believed to promote the GTP‐bound form (N388K) caused accelerated degradation. Conclusion A region encompassing a putative effector‐binding domain (G1‐Deg) is required for Gα degradation via the N‐end rule pathway. Our studies have shown that Gα is susceptible to proteolysis soon after synthesis. These results are in agreement with the idea that Gα is more unstable in the GTP‐bound form, which is the predominant state of monomeric/free Gα soon after synthesis. It is likely that the signal transduced by Gβγ can be regulated by adjusting the levels of Gα through proteolysis.