Protein intrinsically disordered regions (IDRs) play important biological roles despite lacking stable structures. IDRs drive the formation of both biomolecular condensates via liquid–liquid phase separation (LLPS) and solid fibrous amyloid aggregates. Amyloids can be pathogenic and may exhibit self-perpetuating (prion) properties. Relationships between LLPS and the amyloid-forming and prion-propagating abilities of IDRs remain poorly understood. The N-proximal IDR of the yeast translation termination factor eRF3 (Sup35) can form both liquid condensates and heritable amyloid-based prions and serves as a powerful model for investigating these phenomena due to the availability of simple phenotypic, cytological and biochemical assays. Deletion analysis demonstrates that the N-proximal prion domain (Sup35N) of Sup35 is sufficient for chaperone-dependent prion propagation and that various regions of this domain show differential impacts on LLPS, amyloid aggregation, and prion inheritance. Specifically, the N-terminal NQ-rich stretch and the region of oligopeptide repeats are the most important contributors to the LLPS and formation of amyloid fibrils, while oligopeptide repeats and the C-terminal region of Sup35N are crucial for prion inheritance. Contrary to previous reports, the NQ-rich stretch is not required for prion formation and inheritance in yeast. Our data indicate that, in addition to amino acid composition, specific sequence motifs control reversible and heritable assemblies of Sup35.

More than 30% of all human malignancies are brought about by mutations in RAS proto-oncogenes (HRAS, KRAS, and NRAS) that are greatly conserved in yeast RAS1 and RAS2. This makes yeast (Saccharomyces cerevisiae) an efficient single-celled eukaryotic model organism to study their functions. In the current investigation, the null mutation of the RAS2 gene was analyzed to find out its deleterious consequences in yeast cells based on their ability to utilize glycerol as a respiratory substrate, mtDNA mutation rate, mtDNA abundance, and distribution pattern. Mutant cells grown in YPEG plates demonstrated slight respiratory deficiency compared to the wild type. An erythromycin-resistant assay was carried out to analyze the spontaneous mitochondrial DNA mutation rate in the Δras2 mutant and it was found to be greater than that of wild type. In addition, the mitochondrial DNAs of both strains were also visualized under a fluorescence microscope using DAPI fluorescent stain. It was observed that mtDNA abundance was much lower compared to wild type cells. Thus, the present investigation revealed that deletion of the RAS2 gene resulted in mtDNA mutation and depletion.