Alternative CUG Codon Usage in the Halotolerant Yeast : Gene Expression Profiles Provide New Insights into Ambiguous Translation.

The halotolerant yeast belongs to the CTG-Ser1 clade of fungal species that use the CUG codon to translate as leucine or serine. The ambiguous decoding of the CUG codon is relevant for expanding protein diversity, but little is known about the role of leucine-serine ambiguity in cellular adaptations to extreme environments. Here, we examine sequences and structures of tRNA from the CTG-Ser1 clade yeasts, finding that conserves the elements to translate ambiguously. Then, we show that has tolerance to conditions of salinity, acidity, alkalinity, and oxidative stress associated with phenotypic and ultrastructural changes. In these conditions, we found differential expression in both the logarithmic and stationary growth phases of tRNA, tRNA, tRNA, LeuRS, and SerRS genes that could be involved in the adaptive process of this yeast. Finally, we compare the proteomic isoelectric points and hydropathy profiles, detecting that the most important variations among the physicochemical characteristics of proteins are in their hydrophobic and hydrophilic interactions with the medium. We propose that the ambiguous translation, i.e., leucylation or serynation, on translation of the CUG-encoded residues, could be linked to adaptation processes in extreme environments.