Observation of Amyloid-Like Fibers of the Sup35 Protein from Saccharomyces Cerevisiae

In the yeast Saccharomyces cerevisiae, [PST] acts as an epigenetic modifier of translation termination efficiency. [PSI + ] can be passed through generations of yeast cells via changes in protein conformation rather than changes in DNA or RNA, and has thus been referred to as a yeast prion. The [PSI + ] determinant is the Sup35 protein. Sup35 can exist in two states - soluble and insoluble. Soluble Sup35 functions in translation termination, but when insoluble, stop codons are read through, resulting in incorrect protein products. Sup35 is composed of three distinct domains, N, M, and C. The N region is rich in glutamine and asparagine and is required for the [PST] phenotype to exist. M is a highly charged domain, and no specific function has been assigned to it. C is essential in yeast, as it is responsible for translation termination. The insoluble form of Sup35 has characteristics reminiscent of other prion proteins - in vitro it binds to the dye Congo Red and it exhibits apple green birefringence in polarized light.