The extrachromosomal control of nonsense suppression in yeast: an analysis of the elimination of [psi+] in the presence of a nuclear gene PNM.

When a [psi-] strain of yeast mutates to [psi+], the efficiency of suppression by certain ochre suppressors is increased. The [psi+] phenotype is inherited extrachromosomally. There is a nuclear gene, PNM, which, when mutant, causes loss of the [psi+] phenotype. PNM- is dominant to PNM+ and a heterozygous diploid gradually loses the ability over successive generations, to produce PNM+ [psi+] spores. This paper describes the kinetics of this elimination and the data obtained are discussed in relation to two models of the molecular nature of the [psi] genetic determinant--one considering the [psi] determinant as an autonomous nucleic acid, the other treating the possibility that the [psi] nucleic acid is that which codes for rRNA in the nuclear genome.