Characterization of new mutants in the 16s ribosomal subunit region of the Mitochondrial genome of Saccharomyces Cerevisiae.
In Saccharomyces cerevisiae, the ribosomal region of the mitochondrial DNA codes for a 16S rRNA and a 21S rRNA, the rRNA components of the small and large subunits of the mitochondrial ribosomes. However, all mitochondrial ribosomal proteins, with one exception are encoded by nuclear DNA. Hence, the assembly of mitochondrial ribosomes raises interesting questions regarding the interactions between the nuclear and mitochondrial gene products. Paromomycin resistance in S. cerevisiae may result from mutations at the par 1 locus. In this study, paromomycin resistant (PR) mutants were generated using manganese mutagenesis and the mitochondrial mutants were tested for allelism. Three additional new PR strains were constructed from the manganese mutants. Interestingly, 58% of our mutants were nuclear suggesting paromomycin resistance can be influenced by nuclear mutations in presumed mitochondrial ribosomal protein genes. Allelism tests of the mitochondrial mutants indicate some of our mutants are non-allelic. In this study, there was a lack of strong PR mutants in contrast to those usually generated in the 21S rRNA. This suggests that the fidelity of the rRNA gene may not be as important for antibiotic binding in the 16S rRNA in comparison to the 21S rRNA. This hypothesis is supported by studies in the homologous E.coli gene where disruptions in the secondary structure of the 16S rRNA have been shown to affect paromomycin binding. The characterization of new paromomycin resistant mutations in the 16S rRNA gene will help in studies of new mutations affecting the binding of antibiotics to the mitochondrial ribosome. Further genetic studies in conjunction with new biochemical methods for characterizing the rRNA molecule, will help to expand our current knowledge on the relationship between gene sequence, organelle function, protein synthesis and antibiotic binding.