Novel Non-Mendelian Determinant Involved in the Control of Translation Accuracy in Saccharomyces cerevisiae

Corresponding author: Ludmila N. Mironova, St. Petersburg State University, Universitetskaya nab., 7/9, 199034 St. Petersburg, Russia., mila{at}lm2016.spb.edu (E-mail)

Communicating editor: J. RINE

Two cytoplasmically inherited determinants related by their manifestation to the control of translation accuracy were previously described in yeast. Cells carrying one of them, [PSI⁺], display a nonsense suppressor phenotype and contain a prion form of the Sup35 protein. Another element, [PIN⁺], determines the probability of de novo generation of [PSI⁺] and results from a prion form of several proteins, which can be functionally unrelated to Sup35p. Here we describe a novel nonchromosomal determinant related to the SUP35 gene. This determinant, designated [ISP⁺], was identified as an antisuppressor of certain sup35 mutations. We observed its loss upon growth on guanidine hydrochloride and subsequent spontaneous reappearance with high frequency. The reversible curability of [ISP⁺] resembles the behavior of yeast prions. However, in contrast to known prions, [ISP⁺] does not depend on the chaperone protein Hsp104. Though manifestation of both [ISP⁺] and [PSI⁺] is related to the SUP35 gene, the maintenance of [ISP⁺] does not depend on the prionogenic N-terminal domain of Sup35p and Sup35p is not aggregated in [ISP⁺] cells, thus ruling out the possibility that [ISP⁺] is a specific form of [PSI⁺]. We hypothesize that [ISP⁺] is a novel prion involved in the control of translation accuracy in yeast.

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