Sup35p

Sup35p is the Saccharomyces cerevisiae (a yeast) eukaryotic translation termination factor. More specifically, it is the yeast eukaryotic release factor 3 (eRF3), which forms the translation termination complex with eRF1 (Sup45p in yeast). This complex recognizes and catalyzes the release of the nascent polypeptide chain when the ribosome encounters a stop codon. While eRF1 recognizes stop codons, eRF3 facilitates the release of the polypeptide chain through GTP hydrolysis.

Partial loss of function results in nonsense suppression, in which stop codons are ignored and proteins are abnormally synthesized with carboxyl terminal extensions. Complete loss of function is fatal.

Sup35p is an intensely studied protein because it can propagate in a prion form, resulting in the [PSI+] phenotype. Aggregation of Sup35p results in increased nonsense suppression. Several recent journal articles have suggested that the ability to interconvert between [PSI+] and [psi-](prion-free) states provides an evolutionary advantage, but this remains an area of much debate.