Novel genetic and epigenetic suppressors of nonsense mutations in Saccharomyces cerevisiae

Abstract

Nonsense suppression is a process that involves the inhibition of the phenotypic manifestation of nonsense mutations. Typically, nonsense suppression occurs due to a decrease in the translation termination fidelity, which results in the read-through of premature termination codons. This process is important not only for basic purposes but also in biomedical studies because a large number of human heritable diseases and cancers are associated with nonsense mutations. The study of nonsense suppression in yeast began in 1960th and since that time, it was shown the nonsense suppression in yeast is controlled not only by genetic but also by epigenetic factors, prions, representing self-perpetuating infectious protein conformations. Here we demonstrated that novel non-chromosomal determinant [NSI+], previously discovered in our laboratory, possesses main features of yeast prions including dominance, non-chromosomal inheritance during meiosis, reversible curability, and cytoplasmic infectivity. We showed that [NSI+] causes a decrease in translation termination fidelity and has pleiotropic phenotypic manifestation, which is modulated by SUP35, SUP45, and VTS1 genes. [NSI+] was shown to cause nonsense suppression in strains expressing different variants of SUP35-encoding release factor eRF3 with decreased functional activity, but does not affect nonsense suppression in strains producing full-length Sup35. Taking these data into consideration, we proposed that modifications of Sup35 affecting its functional activity create a specific genetic background that allows the identification of novel suppressors. Using such a background, we performed a search for novel genetic and epigenetic suppressors in Saccharomyces cerevisiae. This search was very effective: we described nine novel genetic suppressors (ABF1, GLN3, FKH2, MCM1, MOT3, NAB2, NAB3, REB1, and VTS1). We demonstrated that the overexpression of VTS1 is a phenocopy of [NSI+]. Similarly to [NSI+], the overexpression of VTS1 causes the read-through of termination codons and defects in the vegetative growth. The obtained data expand the knowledge on the modulation of nonsense suppression in S. cerevisiae and suggest that the system of translation termination contains a number of precisely interacting genetic and epigenetics regulators.