Hsp104-dependent ability to assimilate mannitol and sorbitol conferred by a truncated Cyc8 with a C-terminal polyglutamine in Saccharomyces cerevisiae

Abstract

Tup1-Cyc8 (also known as Tup1-Ssn6) is a general transcriptional corepressor. D-Mannitol (mannitol) and D-sorbitol (sorbitol) are the major polyols in nature. Budding yeastSaccharomyces cerevisiaeis unable to assimilate mannitol or sorbitol, but acquires the ability to assimilate mannitol due to a spontaneous mutation inTUP1orCYC8. In this study, we found that spontaneous mutation ofTUP1orCYC8also permitted assimilation of sorbitol. Some spontaneous nonsense mutations ofCYC8produced a truncated Cyc8 with a C-terminal polyglutamine. The effects were guanidine hydrochloride-sensitive and were dependent on Hsp104, but were complemented by introduction ofCYC8, ruling out involvement of a prion. Assimilation of mannitol and sorbitol conferred by other mutations ofTUP1orCYC8was guanidine hydrochloride-tolerant. It is physiologically reasonable thatS.cerevisiaecarries this mechanism to acquire the ability to assimilate major polyols in nature.