Heterologous expression and functional analysis of the F-box protein Ucc1 from other yeast species in Saccharomyces cerevisiae.

The ubiquitin-proteasome system plays an important role in metabolic regulation. In a previous study, we reported that, in Saccharomyces cerevisiae, when glucose is available, the SCFUcc1 ubiquitin ligase complex targets citrate synthase 2 (Cit2) for proteasomal degradation, thereby suppressing the glyoxylate cycle, an anabolic pathway that replenishes the TCA cycle with succinate for the activation of gluconeogenesis. However, the roles of Ucc1 in other yeast species remain unclear. Here, we cloned orthologs of the F-box protein Ucc1 from Zygosaccharomyces bailii, an aggressive food spoilage microorganism that is the most acetic acid-tolerant yeast species, and Candida glabrata, an emerging fungal pathogen. These orthologs were expressed in S. cerevisiae, and their activities were tested genetically and biochemically. The results showed that Z. bailii Ucc1 rescued the ucc1Δ phenotype, suggesting the existence of a similar mechanism regulating the glyoxylate cycle in Z. bailii. By contrast, C. glabrata Ucc1 did not complement the ucc1Δ phenotype or exhibit a dominant negative effect on Ucc1. These results suggest the importance of analysing the regulatory mechanisms of glyoxylate cycle in a broad range of yeast species.