Dosage-Dependent Modifiers of Psi-Dependnet Omnipotent Suppression in Yeast

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S. cerevisiae codon-nonspecific (omnipotent) suppressors, like E. coli ram and tuf mutations (Gorini 1974; Vijgenboom et al. 1985), affect translational fidelity, therefore they are useful for understanding the mechanism of eucaryotic translation. The efficiency of omnipotent suppressors vary between loci and to some extent within a locus; some act as suppressors, and others as allosuppressors. In order to elucidate omnipotent suppression, some omnipotent suppressors or their wild type alleles have been cloned (cf Hinnebusch and Liebman 1991). One of the most interesting and surprising outcomes of such works is that the cloned wild type genes manifest omnipotent suppressor activity by themselves (Liebman et al. 1988; Song et al. 1989; Kushnirov et al. 1990; Chernoff et al. 1991, 1992). It is therefore interesting to see how wild type genes are involved in translational fidelity. From this viewpoint, we began to look for wild type genes that affect the efficiency of sup111 when their dosage is changed by cloning. In this study, we used sup111 because it was one of the least efficient omnipotent suppressors and appeared to be useful for studying gene interactions; sup111 acts as a weak omnipotent suppressor in the psi+ cytoplasm (Ono et al. 1982, 1986) and as an allosuppressor in the psi− cytoplasm (Ono et al. 1991). Our another aim was to clone the wild type SUP111 gene to study its role in translation. Here, we describe the results of our work and present a model for omnipotent suppression.