A Regulatory Role of the Rnq1 Nonprion Domain for Prion Propagation and Polyglutamine Aggregates

Abstract

Prions are transmissible agents caused by the self-propagating conformational change of proteins (32). Prions appear to be amyloid protein aggregates that propagate by capturing soluble proteins and converting them into an infectious aggregated form (33). According to the "protein only" hypothesis (32), the prion protein (PrP) is the sole agent responsible for causing numerous infectious diseases, including scrapie (sheep), bovine spongiform encephalopathy (cow), and chronic wasting disease (deer and elk) as well as kuru and Creutzfeld-Jacob disease (humans Het-s] in Podospora anserina, have also been characterized as non-Mendelian inheritable elements (7,37,43). Molecular and genetic studies of these fungal prions have greatly facilitated the elucidation of the molecular basis for prion conversion and propagation as well as the general criteria for prionogenicity in a protein's primary structure.[PSI ϩ ] is a prion form of Sup35, which is the eRF3 polypeptide release factor that is essential for terminating protein synthesis at stop codons (39, 45; for a review, see reference 17). When Sup35 is in the [PSI ϩ ] state, ribosomes often fail to release polypeptides at stop codons, causing a non-Mendelian trait to appear that is easily detected by nonsense suppression (23,29,30). To uncover host factors responsible for [PSI ϩ ] propagation, we have developed a genome-wide genetic selection method for [PSI ϩ ]-eliminating factors or mutants by use of the chromosomal ura3-197 mutant (21). Based on this selection system, we have selected host factors whose high-level expression on a multicopy plasmid leads to [PSI ϩ ] elimination. One clone yielded Rnq1⌬100, an N-terminal truncation of Rnq1, and is further examined in this study. Although there are some reports that the maintenance or de novo appearance of one prion is affected by several genetic manipulations such as overexpression of its own prion domain (15, 16), heterologous prion variants (5, 35), or nonprion protein mutants (1), the molecular basis of the action of one prion in inhibiting heterologous prions is not known.Rnq1 is a protein of unknown function and is one of several known yeast proteins containing a QN-rich prion domain, where the name derives from "rich in asparagine (N) and glutamine (Q)" (37 . According to the seeding model, a heterologous preexisting protein in the prion conformation is used as a template for the conversion of Sup35 into its prion form, which then proceeds to seed its own rapid and separate aggregation. Importantly, [PIN ϩ ] also facilitates the de novo appearance of the prion [URE3] and promotes polyglutamine (polyQ) aggregation and toxicity in general (5,25,27). Therefore, the seeding model predicts that [PIN ϩ ] aggregates provide a "friendly" nidus on which the first seeds of a heterologous prion or polyQ amyloid can form (11,41). The alternative titration model postulates that preexisting heterologous prions or prion-like aggregates capture and inactivate an inhibitor that prevents conversion of Sup35 into a

Chaperone Proteins Select and Maintain [PIN+] Prion Conformations in Saccharomyces cerevisiae

“…Cpr7p, for example, has intrinsic proline isomerase activity (52,53). Rnq1p contains three proline residues: one in the N-terminal region, a region shown to affect prion propagation (54), and two in a putative loop region between the ␤-sheets of the amyloid core (55). Isomerization of these prolines could potentially affect Rnq1p conformation.…”

A bipolar personality of yeast prion proteins

“…1). In fact, Rnq1 and Rnq1Δ100 were partially co-localized with Sup35 in [RNQ + ], 19,56 and Gpg1 was also co-localized with Sup35 aggregates. 20 However, the growing …”

The Type I Hsp40 Ydj1 Utilizes a Farnesyl Moiety and Zinc Finger-like Region to Suppress Prion Toxicity

“…Overexpression of Rnq1 kills yeast in the presence of [RNQ ϩ ] seeds, yet toxicity is associated with the accumulation of off-pathway, non-amyloid forms of Rnq1 (4). Rnq1 has an N-terminal non-prion domain with no known enzymatic function although it appears to regulate the conversion of native Rnq1 into the [RNQ ϩ ] prion (25). * This work was supported, in whole or in part, by National Institutes of Health Pre-doctoral Training Grant 5T32GM008581-09 (to D. W. S.) and Grant 5R01GM067785-06 (to D. M. C.).…”