Comparison of mammalian mitochondrial ribosomal ribonucleic acid from different species

Abstract

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 degrees C or an ionic strength of 0.01 at 3-4 degrees 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 3.8x10(5)-4.3x10(5) and 5.9x10(5)-6.8x10(5), depending on the technique used. At 25 degrees 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.

Electrophoretic and centrifugation behaviour of mitochondrial ribonucleic acid from Walker 256 carcinosarcoma

“…The values for their electrophoretic mobilities and the equivalent sedimentation coefficients were respectively 20.5 Se and 19.5S, 16.3S, and 16.2S, and 15.4S, and 13.8S. The differences for each RNA species between the S and S. values may represent conformational changes due to the influence of the lower ionic strength used in polyacrylamide-gel electrophoresis (Groot et al, 1970;Mitra et al, 1972).…”

“…Rounding off the Se, values to 20 and 15 respectively, they are nearly identical with the values reported by Groot et al (1970) and Bartoov et al (1970) for rat liver mitochondrial RNA, and something similar occurs with our 15 and 14S values when compared with the 16 and 13S peaks obtained by the same authors. Groot et al (1970) and Mitra et al (1972) showed that the discrepancy between the S and S, values of the larger RNA in rat liver were due simply to conformational changes occurring during electrophoresis, and which were evident by carrying out the runs at different temperatures and ionic strengths. In the case of Walker carcinoma this explanation cannot account either for the presence of both 20 and 16S.…”