Altered ribosomal proteins in emetine resistant strains in the fungus Podospora anserina.

Emetine resistant mutants have been isolated in the fungus Podospora anserina. Genetic analysis of 75 mutants has shown that resistance is controlled by at least two genes, EmR1 and EmR2. In vitro studies showed that resistance to emetine in EmR1 and EMR2 mutants was due to alterations in the protein synthesis machinery. Reconstitution experiments with ribosomal subunits prepared from wild-type and resistant strains indicated that emetine resistance is associated with the 40S subunit.The strains resistant to emetine are also hypersensitive to anisomycin in vivo. In poly-U directed polyphenylalanine synthesis or run off of polysomes, it was shown that mutant ribosomes do not differ from those of wild-type with regard to anisomycin sensitivity, pointing out that initiation would be lso an anisomycin target. The ribosomal proteins isolated from resistant mutants were analyzed by two dimensional gel electrophoresis and compared with the proteins of wild-type ribosomes. The EmR40 mutant was found to have an altered S14 protein. In EmR69, three proteins of the small subunit S13, S15 and S17 were altered, nevertheless only altered S13 and S17 proteins segregate with the resistance character. The comparison of proteolytic digestion of S13 and S17 on SDS gel allowed us to conclude that S13 and S17 would be homologous proteins.