Polymorphism of mitochondrial DNA (mtDNA) in cattle and buffaloes

Mitochondrial DNA (mtDNA) from two breeds of cattle, viz., [Hariana (Bos indicus), Holstein (Bos taurus)] and Indian water buffalo (Bubalis bubalus), was analyzed using 13 restriction endonucleases which recognized an average of about 40 six-base sites. Polymorphism among cattle was detected with six of these enzymes. The two Holstein differed at six sites, whereas the Hariana breed (Bos indicus) did not show any site polymorphism. Surprisingly, the Hariana type differed by only one site from one of the Holstein types. The total size of buffalo mtDNA was estimated to be 16.4 kb. Polymorphism within the Murrah buffalo breed was observed with respect to aBglI site. Scarcely any of the restriction fragments of buffalo mtDNA matched those of cattle mtDNA.     

Nucleotide sequence of Rattus norvegiens mitochondrial DNA that includes the genes for tRNAile, tRNAgln and tRNAf-met

The nucleotide sequence of a segment of mtDNA from Rattus norvegiens (rat) which contains the genes for tRNA^ile, tRNA^gl and tRNA^f-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNA^ile, tRNA^gln and tRNA^f-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.     

Isolation and characterization of nuclear genes coding for subunits of the yeast ubiquinol-cytochrome c reductase complex

Nuclear genes coding for the M_r 17000, 14000 and 11000 subunits of the ubiquinol-cytochrome c reductase complex (complex III) in yeast have been isolated from a clone bank of yeast nuclear DNA by use of a mRNA hybridization-competition assay. This is based on our observations that levels of mRNAs for these subunits are much reduced during glucose repression and in cytoplasmic petite mutants and the procedure should be of general application for the isolation of other inducible or repressible genes coding for mRNAs present at low levels in the cell. A first characterization of the clones is presented. The genes are not closely linked in the genome and those coding for M_r 14000 and 11000 subunits are present in unique genomic environments, which suggests that there are only single copies of each in the nuclear genome.     

Yeast mitochondrial and cytoplasmic valyl-tRNA synthetases

Yeast mitochondrial tRNA synthetase has been partially purified and chromatographic, catalytic and antigenic properties have been compared to the cytoplasmic homologous enzyme from yeast. No significant differences could be observed between the two enzymes with respect to their behaviour during ammonium sulfate precipitation or in chromatographic separation on DEAE cellulose, hydroxylapatite and Sephadex G 200. The Km of the two enzymes toward tRNAs from yeast mitochondria, yeast cytoplasm or E. coli are pratically identical. The antigenic properties of the two enzymes are very similar; antisera against either the mitochondria or the cytoplasmic enzyme lead to the inhibition of their catalytic properties. The mitochondrial ValRS is formed by a single polypeptide chain whose molecular weight is 125,000 daltons, a value very close to that of the yeast cytoplasmic enzyme.     

Control of activity states of heart mitochondrial ATPase. Role of the proton-motive force and Ca2+

The ATPase complex of submitochondrial particles exhibits activity transitions that are controlled by the natural ATPase inhibitor (Gómez-Puyou, A., Tuena de Gómez-Puyou, M. and Ernster, L. (1979) Biochim. Biophys. Acta 547, 252–257). The ATPase of intact heart mitochondria also shows reversible activity transitions; the activation reaction is induced by the establishment of electrochemical gradients, whilst the inactivation reaction is driven by collapse of the gradient. In addition it has been observed that the influx of Ca²⁺ into the mitochondria induces a rapid inactivation of the ATPase; this could be due to the transient collapse of the membrane potential in addition to a favorable effect of Ca²⁺-ATP on the association of the ATPase inhibitor peptide to F₁-ATPase. This action of Ca²⁺ may explain why mitochondria utilize respiratory energy for the transport of Ca²⁺ in preference to phosphorylation. It is concluded that the mitochondrial ATPase inhibitor protein may exert a fundamental regulatory function in the utilization of electrochemical gradients.     

Binding of ADP to beef-heart mitochondrial ATPase (F1)

1. ADP binding to beef-heart mitochondrial ATPase (F₁), in the absence of Mg²⁺, has been determined by separating the free ligand by ultrafiltration and determining it in the filtrate by a specially modified isotachophoretic procedure.2. Since during the binding experiments the ‘tightly’ bound ADP (but not the ATP) dissociates, it is necessary to take this into account in calculating the binding parameters.3. The binding data show that only one tight binding site (K_d about 0.5 μM) for ADP is present.4. It is not possible to calculate from the binding data alone the number of or the dissociation constants for the weak binding sites. It can be concluded, however, that the latter is not less than about 50 μM.     

Recombinant DNA analysis indicates that the multiple chromosomes of maize mitochondria contain different sequences

Twenty-eight Bam H 1 restriction fragments were isolated from normal mitochondrial DNA of maize by recombinant DNA techniques to investigate the organization of the mitochondrial genome. Each cloned fragment was tested by molecular hybridization against a Bam digest of total mitochondrial DNA. Using Southern transfers, we identified the normal fragment of origin for d each clone. Twenty-three of the tested clones hybridized only to the fragment from which the clone was derived. In five cases, labeling of an additional band indicated some sequence repetition in the mitochondrial genome. Four clones from normal mitochondrial DNA were found which share sequences with the plasmid-like DNAs, S-1 and S-2, found in S male sterile cytoplasm. The total sequence complexity of the clones tested is 121×10⁶ d (daltons), which approximates two thirds of the total mitochondrial genome (estimated at 183×10⁶ d). Most fragments do not share homology with other fragments, and the total length of unique fragments exceeds that of the largest circular molecules observed. Therefore, the different size classes of circular molecules most likely represent genetically discrete chromosomes in a complex organelle genome. The variable abundance of different mitochondrial chromosomes is of special interest because it represents an unusual mechanism for the control of gene expression by regulation of gene copy number. This mechanism may play an important role in metabolism or biogenesis of mitochondria in the development of higher plants.