Novel
antisuppressor determinant [ ASP + ] of the yeast Saccharomyces
cerevisiae.
Veniamin A. Startsev, Julia V. Sopova, Sergey P. Zadorsky, Sergey G.
Inge-Vechtomov
Dep. of Genetics and Breeding, St-Petersburg State University, Universitetskaja
nab, St-Petersburg, 199034, Russia (startsev@pochtamt.ru)
Recently identified presumed prion [ISP+] is antisuppressor toward the sup35-10 and sup35-25 nonsense suppressor alleles of the SUP35 gene coding for translation termination factor eRF3. We discovered novel antisuppressor determinant in the transgenic S. cerevisiae strains with SUP35 gene substituted for its homologue from Pichia methanolica possessing a suppressor phenotype. Novel determinant had an antisuppressor effect relative to Pichia SUP35 gene and was designated as [ASP+] from Antisuppressor to SUP35 of Pichia. [ASP+] was lost upon growth on media containing GuHCL and manifestated dominantly in hybrids from crossing [ASP+] and [asp-] strains. [ASP+] showed unstable inheritance in meiosis but the presence of tetrads with 4 [ASP+]: 0 [asp-] segregation may indicate extrachromosomal inheritance of [ASP+]. [ASP+] is maintained and manifestates on a background of the sup35-25 suppressor allele. This could mean that [ASP+] and [ISP+] represent the same cytoplasmic factor. We estimated the nonsense suppression efficiency in hybrids obtained by crossing isogenic strains [ASP+] and [asp-] with isogenic strains [ISP+] and [isp-], all of them bearing sup35-25 allele. We registered the additivity of antisuppressor effects of [ASP+] and [ISP+] in the [ASP+] [ISP+] hybrid possessing the least suppression efficiency of hybrids studied. The data obtained testify that [ASP+] may represent one more cytoplasmic factor (possibly, prion) distinct from [ISP+]. Supported by CRDF ST-012-0.