Conservative system for dosage-dependent modulation of translational fidelity in eukaryotes

Abstract

Variations in dosage of some genes can alter the level of translational fidelity. The Saccharomyces cerevisiae genes that act as dosage-dependent suppressors and/or modulators of suppression, are the following: some tRNA genes (for example, tRNA Gln) inducing readthrough by mispairing; genes coding for either translational elongation factor or other proteins taking part in translation; and some genes of unknown function. We suggest that the SUP35 protein is a factor which may play a major role in balance-dependent regulation of translational fidelity. Homologues of this genes have been identified in other yeast genera ( Pichia), green algae ( Chlamydomonas) and various animals including man. No homologies have been found in the polychaeta ( Nereis) or in insects ( Drosophila). Rates of evolution differ for two separate parts of the genes; the N-terminal part, which is important for ambiguous translation in Saccharomyces, is markedly variable in the organisms tested. However, the C-terminal part which is required for yeast viability has a common origin but a separate evolution from that of the EF-Tu protein family.