In vitro nonsense suppression in [psi+] and [psi-] cell-free lysates of Saccharomyces cerevisiae.

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Abstract
An homologous in vitro assay for yeast nonsense suppressors was used to examine the effect of the cytoplasmically inherited genetic determinant [psi] on the efficiency of in vitro nonsense suppression. The efficiency of all 3 types of yeast tRNA-mediated nonsense suppressor (ochre, amber and UGA) is much greater in cell-free lysates prepared from a sup+ [psi+] strain than in lysates prepared from an isogeneic sup+ [psi-] strain. Lysates prepared from a [psi-] strain, into which the [psi+] determinant was reintroduced by kar1-mediated cytoduction, support efficient suppression. Evidence is presented that [psi-] lysates contain an inhibitor of in vitro nonsense suppression.