Comparison of mammalian mitochondrial ribosomal ribonucleic acid from different species

Mitochondrial ribosomal RNA species from mouse L cells, rat liver, rat hepatoma, hamster BHK-21 cells and human KB cells were examined by electrophoresis on polyacrylamide–agarose gels and sedimentation in sucrose density gradients. The S_E (electrophoretic mobility) and S values of mitochondrial rRNA of all species were highly dependent on temperature and ionic strength of the medium; the S_E values increased and the S values decreased with an increase in temperature at a low ionic strength. At an ionic strength of 0.3 at 23–25°C or an ionic strength of 0.01 at 3–4°C the S and S_E values were almost the same being about 16.2–18.0 and 12.3–13.6 for human and mouse mitochondrial rRNA. The molecular weights under these conditions were calculated to be 3.8×10⁵–4.3×10⁵ and 5.9×10⁵–6.8×10⁵, depending on the technique used. At 25°C in buffers of low ionic strength mouse mitochondrial rRNA species had a lower electrophoretic mobility than those of human and hamster. Under these conditions the smaller mitochondrial rRNA species of hamster had a lower electrophoretic mobility than that of human but the larger component had an identical mobility. Mouse and rat mitochondrial rRNA species had identical electrophoretic mobilities. Complex differences between human and mouse mitochondrial rRNA species were observed on sedimentation in sucrose density gradients under various conditions of temperature and ionic strength. Mouse L-cell mitochondrial rRNA was eluted after cytoplasmic rRNA on a column of methylated albumin–kieselguhr.