Amyloid and Amyloid-Like Aggregates: Diversity and the Term Crisis.

Active accumulation of the data on new amyloids continuing nowadays dissolves boundaries of the term "amyloid". Currently, it is most often used to designate aggregates with cross-ß structure. At the same time, amyloids also exhibit a number of other unusual properties, such as: detergent and protease resistance, interaction with specific dyes, and ability to induce transition of some proteins from a soluble form to an aggregated one. The same features have been also demonstrated for the aggregates lacking cross-ß structure, which are commonly called "amyloid-like" and combined into one group, although they are very diverse. We have collected and systematized information on the properties of more than two hundred known amyloids and amyloid-like proteins with emphasis on conflicting examples. In particular, a number of proteins in membraneless organelles form aggregates with cross-ß structure that are morphologically indistinguishable from the other amyloids, but they can be dissolved in the presence of detergents, which is not typical for amyloids. Such paradoxes signify the need to clarify the existing definition of the term amyloid. On the other hand, the demonstrated structural diversity of the amyloid-like aggregates shows the necessity of their classification.

[Identification of new genes that affect [PSI

Translation termination is an important step in gene expression. Its correct processing is governed by eRF1 (Sup45) and eRF3 (Sup35) proteins. In Saccharomyces cerevisiae, mutations in the corresponding genes, as well as Sup35 aggregation in [PSI^(+)] cells that propagate the prion form of Sup35 lead to inaccurate stop codon recognition and, consequently, nonsense suppression. The presence of stronger prion variants results in the more efficient suppression of nonsense mutations. Previously, we proposed a synthetic lethality test that enables the identification of genes that may influence either translation termination factors or [PSI^(+)] manifestation. This is based on the fact that the combination of sup45 mutations with the strong [PSI^(+)] prion variant in diploids is lethal. In this work, a set of genes that were previously shown to enhance nonsense suppression was analyzed. It was found that ABF1, FKH2, and REB1 overexpression decreased the growth of strains in a prion-dependent manner and, thus, might influence [PSI^(+)] prion toxicity. It was also shown that the synthetic lethality of [PSI^(+)] and sup45 mutations increased with the overexpression of GLN3 and MOT3 that encode Q/N-rich transcription factors. An analysis of the effects of their expression on the transcription of the release factors genes revealed an increase in SUP35 transcription in both cases. Since SUP35 overexpression is known to be toxic in [PSI^(+)] strains, these genes apparently enhance [PSI^(+)] toxicity via the regulation of SUP35 transcription.

[The identification of Saccharomyces cerevisiae genes leading to synthetic lethality of prion [PSI+] with Sup45 mutations].

Previously, we proposed a test system allowing to perform search for genes that influence the properties of the Sup35 and Sup45 protein. This test is based on the phenomenon of lethality of diploids that combine mutations in SUP45 gene with [PSI+] prion. Lethality of this combination depends on the type of sup45 mutation, and the properties of the prion. [PSI+] variant, which is a strong suppressor ([PSI+]s), showing synthetic lethality with all the nonsense mutations and some missense sup45 mutations in the heterozygote state. The presence of extra copies of a gene under test that affects the phenotypic manifestation of prion [PSI+] or translation termination factors properties, leads to the increase or decrease in diploid lethality. Gene library screening using this test system allowed us to establish the effect of ten fragments of genomic DNA of yeast on synthetic lethality. Deletion analysis of these regions has led to the identification of the HLJ1 and TEF2 genes, as affecting Sup35 protein prionization and/or the efficiency of translation termination.