[Search for the genes critical for propagation of the prion-like antisuppressor determinant [ISP+] in yeast using insertion library].

The prion-like determinant [ISP+] manifests itself as antisuppressor of certain sup35 mutations. To establish that [ISP+] actually represents a new yeast prion, it is necessary to identify the gene encoding protein corresponding in its prion form to [ISP+]. Analysis of transformants obtained by transformation of [ISP+] strain with insertion gene library revealed three genes controlling the [ISP+] maintenance. These genes are UPF1, UPF2 and SFP1. The SFP1 encodes potenlially prionogenic protein, as it is enriched with asparagine and glutamine residues. Therefore it is the most likely candidate to the role of [ISP+] structural gene. The UPF1 and UPF2 products are components of nonsense-mediated mRNA decay. It was shown that [ISP+] elimination caused by UPF1 and UPF2 inactivation is reversible. It was shown also that Upf1 and Upf2 proteins are not related functionally to Ppzlp phosphatase, influencing [ISP+] manifestation. Possible mechanisms of UPF1 and UPF2 influence on [ISP+] maintenance are discussed.