Effects of Ubiquitin System Alterations on the Formation and Loss of a Yeast Prion

• Published in: The Journal of biological chemistry Vol. 282; no. 5; pp. 3004 - 3013
• Main Authors: Allen, Kim D., Chernova, Tatiana A., Tennant, E. Paula, Wilkinson, Keith D., Chernoff, Yury O.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02.02.2007; American Society for Biochemistry and Molecular Biology
• Subjects: Cloning, Molecular; Genes, Reporter; Kinetics; Plasmids; Prions - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - growth & development; Saccharomyces cerevisiae - metabolism; Transfection; Ubiquitin - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M609597200

The yeast prion [PSI+] is a self-propagating amyloidogenic isoform of the translation termination factor Sup35. Overproduction of the chaperone protein Hsp104 results in loss of [PSI+]. Here we demonstrate that this effect is decreased by deletion of either the gene coding for one of the major yeast ubiquitin-conjugating enzymes, Ubc4, or the gene coding for the ubiquitin-recycling enzyme, Ubp6. The effect of ubc4Δ on [PSI+] loss was increased by depletion of the Hsp70 chaperone Ssb but was not influenced by depletion of Ubp6. This indicates that Ubc4 affects [PSI+] loss via a pathway that is the same as the one affected by Ubp6 but not by Ssb. In the presence of Rnq1 protein, ubc4Δ also facilitates spontaneous de novo formation of [PSI+]. This stimulation is independent of [PIN+], the prion isoform of Rnq1. Numerous attempts failed to detect ubiquitinated Sup35 in the yeast extracts. While ubc4Δ and other alterations of ubiquitin system used in this work cause slight induction of some Hsps, these changes are insufficient to explain their effect on [PSI+]. However, ubc4Δ increases the proportion of the Hsp70 chaperone Ssa bound to Sup35, suggesting that misfolded Sup35 is either more abundant or more accessible to the chaperones in the absence of Ubc4. The proportion of [PSI+] cells containing large aggregated Sup35 structures is also increased by ubc4Δ. We propose that UPS alterations induce an adaptive response, resulting in accumulation of the large “aggresome”-like aggregates that promote de novo prion generation and prion recovery from the chaperone treatment.