Biosynthesis of ribonucleic acid in yeast: Some properties of mitochondrial ribosomal ribonucleic acid in Saccharomyces carlsbergensis

Abstract

A study of yeast mitochondrial RNA showed that although this RNA sediments in sucrose density gradients considerably slower than cytoplasmic ribosomal RNA, both RNA species have very similar electrophoretic mobilities on polyacrylamide gels. Denaturation in formaldehyde results in a relatively larger decrease in the rate of sedimentation of mitochondrial RNA than of cytoplasmic ribosomal RNA or Escherichia coli ribosomal RNA. This suggests that hydrogen bonding is relatively more important as a stabilizing factor of the secondary structure of mitochondrial ribosomal RNA than of the latter two RNA species. This result also demonstrates that profound differences exist between mitochondrial ribosomal RNA and bacterial ribosomal RNA. Cycloheximide, a powerful inhibitor of the formation of cytoplasmic ribosomal RNA, was also found to inhibit the formation of the mitochondrial 22S and 15S RNA components. This shows that the formation of these RNA species is controlled by cytoplasmic protein formation. Fractionation of yeast mitochondrial RNA by sucrose density gradient centrifugation followed by hybridization of the individual fractions with mitochondrial and nuclear DNA showed that a considerable degree of homology exists between mitochondrial DNA and a mitochondrial RNA fraction sedimenting at about 19S. This is most likely metabolically stable messenger RNA, and it cannot be concluded from hybridization experiments between total mitochondrial RNA and mitochondrial DNA that mitochondrial ribosomal RNA is transcribed from mitochondrial DNA. Mitochondrial RNA homologous to nuclear DNA was found to sediment as material closely similar to the 22S component. The usefulness of sodium iodide gradients for the fractionation of total yeast DNA into its mitochondrial and nuclear components is described.