Mutations relieving hypersensitivity to paromomycin caused by ribosomal suppressors inPodospora anserina

Abstract

SUMMARY: In the fungusPodospora anserina, mutations were selected which relieved the hypersensitivity to paromomycin caused by four suppressors assumed to be ribosomal ambiguity mutations (su_1–31,su_1–49,su_1–60,su_2–5). Our first purpose was to isolate new antisuppressor mutations and in fact a new antisuppressor gene,AS₇was uncovered. TheAS_7–1mutant displays a pleiotropic phenotype and particularly a sporulation defect. On the other hand, a newsu₁mutant was obtained which acts as a suppressor and also as an antisuppressor: it can specifically reduce the suppressor effect of certainsu₂mutations. This property of somesu₁andsu₂mutations was already known. Apart from these mutations probably involved in the control of translational fidelity, six mutations conferring cross-resistance to paromomycin and neomycin were isolated. While four of them are localized in thePm₁andPm₂loci previously identified, the two others define a new gene which controls paromomycin and neomycin resistance,Pm₃. Strains carrying thePm_3–1allele are sensitive to temperature at the level of growth and sporulation. The three last mutations which were obtained confer no mutant phenotype when separated from thesu₁background. They are closely linked to thesu₂locus.