Physico‐Chemical Properties of Mitochondrial Ribosomal RNA from Fungi

Abstract

Several physico-chemical properties of mitochondrial and cytoplasmic ribosomal RNA from the filamentous fungi, Trichoderma viricle and Neurospora crassa were determined and compared with those for Aspergillus nidulans.1. The thermal denaturation patterns of the mitochondrial rRNAs differed markedly from those of their homologous cytoplasmic rRNAs. The two rRNAs, therefore, possess distinct conformations in solution. 2.The guanine + cytosine content of Trichoderma mitochondrial rRNA was shown to be very low (31.5 and 35.5O/, for the heavy and light components) and to differ considerably from that of its cytoplasmic rRNA (50 and 49 ,Io). Such nucleotide compositions are characteristic of fungal mitochondrial rRNA and account, at least in part, for the unusual physical characteristics which these polynucleotides exhibit.3. Polyacrylamide gel electrophoresis of mitochondrial and cytoplasmic rRNA was performed in buffers of different ionic strenghts. I n low-salt buffer, the relative mobilities of the mitochondrial rRNAs were severely retarded, causing mitochondrial rRNA to migrate more slowly than cytoplasmic rRNA. I n Mg buffer, mitochondrial and cytoplasmic rRNA co-electrophoresed and were easily distinguished from Escherichia coli rRNA. Thus, under certain conditions, the conformational peculiarities of fungal mitochondrial rRNAs are expressed with this technique as well. It is concluded that accurate extrapolations from electrophoretic mobilities to molecular weight values cannot be made for these rRNA samples.4. Mitochondrial rRNAs sediment more slowly than their corresponding cytoplasmic rRNAs. However, under the same experimental conditions the sedimentation velocity patterns for the various mitochondrial rRNAs are not identical.5. While the above measurements clearly distinguish mitochondrial rRNAs, as a group, from cytoplasmic and bacterial rRNAs, they also point out a considerable physical heterogeneity among the fungal mitochondrial rRNAs.I n previous reports we have described several physical and chemical characteristics of mitochondrial ribosomal RNA from the fungus, Aspergillus nidulans. Observations relating to size, conformation, nucleot,ide coniposition and nucleotide distribution have revealed that mitochondrial rRNA in this fungus differs markedly not only from its homologous cytoplasmic rRNA but from bacterial-type rRNA as well [i -61. In the present report we extend some of these observations to two other filamentous fungi, Trichoderrna viride and Neurospora crassa. In particular, thermally-induced absorbance changes and electrophoretic mobilities on polyacrylamide gels in buffers of different ionic strengths point out the conformational peculiarities of mitochondrial rRNA. These behaviors appear to be linked to the unusually low mole percentage of guanine and cytosine which the fungal mitochondrial rRNAs possess. While the physicochemical measurements serve to clearly distinguish fungal mitochondrial rRNA, as a group, from cytoplasmic and bacterial rRNAs, they also reveal differences among the ...

Maize Mitochondria: Purification and Characterization of Ribosomes and Ribosomal Ribonucleic Acid

“…Low guanine-cytosine content of RNA, which has been reported for soybean (2) and mung bean (17) mitochondrial rRNA, has been shown to result in anomalous slow migration of RNA (19). Others have found relative mobility to be affected by salt and temperature (10,12,14). The formaldehyde approach to mol wt determinations (3) has not been satisfactory in some aspects (10,14,26).…”

Comparison of mammalian mitochondrial ribosomal ribonucleic acid from different species

“…The greater unfolding of mitochondrial rRNA as the temperature increases in buffers of low ionic strength could arise from its lower G + C content which would mean that its hydrogen bonds would 'melt' more readily than those of the G+C rich cytoplasmic rRNA. This has been pointed out by Loening (1969) and has been applied to mitochondrial rRNA of several species by others (Groot et al, 1970;Forrester et al, 1970;Edelman et al, 1971;Grivell et al, 1971).…”

“…Montenecourt et al (1970) found that mitochondrial rRNA species from hamster and mouse differ in electrophoretic mobilities and sedimentation coefficients. The significance of this is unclear because the physical properties of mitochondrial rRNA from mammalian as well as other species is highly dependent on the ionic composition of the solvent and the temperature (Groot et al, 1970;Forrester et al, 1970;Edelman et al, 1971;Grivell et al, 1971). Moreover, a discrepancy exists between the size of the RNA as indicated by the rate of sedimentation and the electrophoretic mobility for mammalian mitochondrial rRNA (Bartoov et al, 1970).…”

Changes in ribonucleases during differentiation (spherulation) of Physarum polycephalum

“…The salt concentration of the electrophoresis buffer and the moderately high "G+C" content of Physarum microsomal RNA (a molar percentage of 54.4). CUMMINS et al (1966) suggest that overestimation of the molecular weights of the rRNA species was not appreciable (LOENING 1969, EDELMAN et al 1971).…”