Mitochondrially encoded resistance to paramomycin in Saccharomyces cerevisiae : Reinvestigation of a controversy

The authors have reinvestigated the nature of mitochondrially inherited resistance to paromomycin in S. cerevisiae . Resistance to this antibiotic can arise by a nucleotide alteration in the gene coding for 15 S ribosomal RNA at a recognition site for the restriction endonuclease ThaI (CGCG). The authors have confirmed this finding and document here also a new type of paromomycin resistance that is unrelated to this ThaI restriction site. This shows that paromomycin resistance can occur in the presence of the ThaI site. After sporulation, suitable paromomycin-resistant haploids were crossed with each other and sensitive recombinant diploids were found, indicating the existence of more than one form of paromomycin resistance. Possible explanations for this novel type of paromomycin resistance and the unorthodox way in which it arises, are presented.