The tRNA-Tyr gene family of Saccharomyces cerevisiae: agents of phenotypic variation and position effects on mutation frequency.
Extensive phenotypic diversity or variation exists in clonal populations of microorganisms and is thought to play a role in adaptation to novel environments. This phenotypic variation or instability, which occurs by multiple mechanisms, may be a form of cellular differentiation and a stochastic means for modulating gene expression. This work dissects a case of phenotypic variation in a clinically derived Saccharomyces cerevisiae strain involving a cox15 ochre mutation, which acts as a reporter. The ochre mutation reverts to sense at a low frequency while tRNA-Tyr ochre suppressors (SUP-o) arise at a very high frequency to produce this phenotypic variation. The SUP-o mutations are highly pleiotropic. In addition, although all SUP-o mutations within the eight-member tRNA-Tyr gene family suppress the ochre mutation reporter, there are considerable phenotypic differences among the different SUP-o mutants. Finally, and of particular interest, there is a strong position effect on mutation frequency within the eight-member tRNA-Tyr gene family, with one locus, SUP6, mutating at a much higher than average frequency and two other loci, SUP2 and SUP8, mutating at much lower than average frequencies. Mechanisms for the position effect on mutation frequency are evaluated.
Ito-Harashima
Sayoko
S
Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Hartzog
Phillip E
PE
Sinha
Himanshu
H
McCusker
John H
JH
D016153:Genes, Suppressor; D014644:Genetic Variation; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D012365:RNA, Transfer, Tyr / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
C107633:COX15 protein, S cerevisiae; D008565:Membrane Proteins; D012365:RNA, Transfer, Tyr; D029701:Saccharomyces cerevisiae Proteins