Suppressor-specificity of antisuppressors in yeast

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

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 three 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 also presented that [psi-] lysates contain an inhibitor of in vitro nonsense suppression.

Ribosomal proteins of yeast strains carrying mutations which affect the efficiency of nonsense suppression

We have examined the ribosomal proteins of strains of Saccharomyces cerevisiae which differ in the efficiency with which ochre nonsense mutations are suppressed. The strains in which ochre suppression is poor were [psi]- or carried antisuppressor mutations; those in which suppression was highly efficient were [psi]+ or carried allosuppressor mutations. The ribosomal proteins of these strains, as judged by two-dimensional polyacrylamide gel electrophoresis, were indistinguishable from those of wild-type.