The size of the repeating unit of the repetitive mitochondrial DNA from a "low-density" petite mutant of yeast

Circular mitochondrial DNA molecules from petite mutants of Saccharomyces cerevisiae: resolution by polyacrylamide gel electrophoresis

Mitochondrial DNA (mtDNA) from petite strain K45 of Saccharomyces cerevisiae contains about 7% circular DNA molecules which comprise a simple oligomeric series based on a monomeric size of 1.7 kilobase pairs. Electrophoresis of K45 mtDNA on a polyacrylamide-agarose slab gel fractionates the mtDNA into a major band (containing linear DNA) and several faster running minor bands each containing particular size class of circular DNA molecules. From study of mtDNA from K45 and two other simple petites it was found that the mobility of circles is inversely proportional to the logarithm of the circle size. Polyacrylamide gel electrophoresis thus permits the separation of circular mtDNA from the linear mtDNA of simple petites, and physically resolves circles of different size from one another.

The nucleotide sequence of two restriction fragments located in the gene AB region of bacteriophage S13

The nucleotide sequence of a double stranded DNA fragment from the gene AB region of bacteriophage S13 DNA has been determined. The fragment was isolated as two adjacent shorter fragments by cleavage of S13 replicative form (RF) DNA with restriction endonuclease III from Hemophilus aegyptius. The strands of the fragments were separated electrophoretically and hydrolyzed with T4 endonuclease IV to yield short oligonucleotides which were then sequenced by partial exonuclease digestion. The complete nucleotide sequence of the restriction fragments was obtained by ordering the inter- and intrastrand overlapping oligonucleotide sequences. The adjacent fragments were 190 nucleotides in length. The sequences included a HindII site, an AluI site and two sequences which may be possible transcription initiation sequences, one with an adjacent sequence homologous to the canonical promoter site sequence T-A-T-Pu-A-T-Pu. Examination of the three possible reading frames for translation of the sequence revealed only one possible complete translation product. The postulated partial sequence of gene A protein has a highly positively charged arginine-rich area which may have importance in DNA binding.

Mitochondrial DNA replication in petite mutants of yeast: resistance to inhibition by ethidium bromide, berenil and euflavine

Mitochondrial DNA (mtDNA) replication in petite mutants of Saccharomyces cerevisiae is generally less sensitive to inhibition by ethidium bromide than in grande (respiratory competent) cells. In every petite that we have examined, which retain a range of different grande mtDNA sequences, this general phenomenon has been demonstrated by measurements of the loss of mtDNA from cultures grown in the presence of the drug. The resistance is also demonstrable by direct analysis of drug inhibition of mtDNA replication in isolated mitochondria. Furthermore, the resistance to ethidium bromide is accompanied, in every case tested, by cross-resistance to berenil and euflavine, although variations in the levels of resistance are observed. In one petite the level of in vivo resistance to the three drugs was very similar (4-fold over the grande parent) whilst another petite was mildly resistant to ethidium bromide and berenil (each 1.6-fold over the parent) and strongly resistant (nearly 8-fold) to inhibition of mtDNA replication by euflavine. The level of resistance to ethidium bromide in several other petite clones tested was found to vary markedly. Using genetic techniques it is possible to identify those petites which display an enhanced resistance to ethidium bromide inhibition of mtDNA replication. It is considered that the general resistance of petites arises because a product of mitochondrial protein synthesis is normally involved in facilitating the inhibitory action of these drugs on mtDNA synthesis in grande cells. The various levels of resistance in petites may be modulated by the particular mtDNA sequences retained in each petite.

Structure of animal mitochondrial DNA (base composition, pyrimidine clusters, character of methylation)

Base composition, content of pyrimidine isopliths and methylation degree of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) from various vertebrates and protozoon Crithidia oncopelti have been studied. mtDNAs from mammals (ox, rat) do not differ in fact in the G + C content from the respective nDNA. The G + C content in mtDNA from fishes (sheat-fish) and birds (duck, chicken) is 1.5--2.5 mol % higher than in the respective nDNA. Kinetoplast DNA (kDNA) from Crithidia oncopelti (G + C = 42.9 mol %) differs significantly in base composition from nDNA (G + C 51.3 mol%). All the mtDNA and kDNA studied differ from the respective nDNA by a lower degree of pyrimidine clustering. The amount of mono- and dipyrimidine fragments in mtDNA is more than 30 mol %, whereas in nDNA it does not exceed 23 mol %. The quantity of long pyrimidine clusters (hexa- and others) is 2--4 times lower in mtDNA than in nDNA. The lower degree of clustering of pyrimidine nucleotides seems to be a specific feature of all the mtDNA studied. This may be indicative of common traits in the organization and origin of mtDNA. All mtDNA of vertebrates contain 5-methylcytosine as "minor" base (1.5--3.15 mol %) and surpass by 1.5--2 times the respective nDNA in the methylation degree. It has been found that in animals mtDNA is species specific as far as the 5-methylcytosine content is concerned. mtDNA of beef heart differs significantly from nDNA in the mode of 5-methylcytosine distribution in pyrimidine isopliths, which may indicate that methylation specificity of nuclear and mitochondrial DNA is not the same. In mitochondria and nuclei of rat liver certain DNA-methylase activity has been detected, which provides in vitro the methylation of cytosine residues both in homologbous DNA and various heterologous DNAs. Specificity of methylation in vitro of cytosine residues in one and the same heterologous DNA from Escherichia coli B with nuclear and mitochondrial enzymes is different. Mitochondrial enzyme methylates cytosine residues chiefly in mono-, whereas nuclear enzyme, in di- and tripyrimidine fragments.

The structure of animal mitochondrial DNA (base composition, pyrimidine clusters, character of methylation)

Base composition, content of pyrimidine isopliths and the degree of methylation of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) from various vertebrates and protozoon Crithidia oncopelti have been studied. MtDNAs from mammals (ox, rat) do not differ in fact in the GC content from the respective nDNA. The GC content in mtDNA from fishes (sheat fish) and birds (duck, chicken) is 1.5-2.5 mole % higher than in the respective nDNA. Kinetoplast DNA (kDNA) from Crithidia oncopelti (GC = 42.9 mole %) differs significantly in base composition from nDNA (GC = 51.3 mole %). All the mtDNA and kDNA studied differ from the respective nDNA by a lower degree of pyrimidine clustering. The amount of mono and dipyrimidine fragments in mtDNA is more than 30 mole %, whereas in nDNA it does not exceed 23 mole %. The quantity of long pyrimidine clusters (hexa and others) is 2-4 times lower in mtDNA than in nDNA. The lower degree of clustering of pyrimidine nucleotides seems to be a specific feature of all the mtDNA studied. This may be indicative of common traits in the organization and origin of mtDNA. All mtDNA of vertebrates contain 5-methylcytosine as a 'minor' base (1.5- 3.15 mole %) and surpass by 1.5-2 times the respective nDNA in the methylation degree. It has been found that in animals mtDNA is species specific as far as the 5-methyl-cytosine content is concerned. In mitochondria and nuclei of rat liver certain DNA methylase activity has been detected, which provides in vitro the methylation of cytosine residues both in homologous DNA and various heterologous DNAs. The specificity of methylation in vitro of cytosine residues in the same heterologous DNA from E. coli B varies with the source of enzymes. The mitochondrial enzyme methylates cytosine as the lone monopyrimidine residue, whereas the nuclear enzyme methylase cytosine in the di- and tripyrimidine fragments.

The binding of poly (rA) and poly (rU) to denatured DNA. II. Studies with natural DNAs

We have studied the interaction of poly(rA) and poly(rU) with natural DNAs containing (dA.dT)n sequences. The results indicate that hybridization of poly(rA) to denatured DNA can be used to estimate the size and frequency of large (dA.dT)n tracts, whereas hybridization with poly(rU) does not give reliable information on these points. In 6.6 M CsCl, poly(rU) can form stable complexes with denatured DNA containing short (dA)n tracts (n less than or equal to 6), whereas binding of poly(rA) to denatured DNA under these conditions requires much larger (dT)n tracts (estimated n greater than 13). Moreover, binding of poly(rA) requires pre-hybridization in low salt, because free poly(rA) precipitates in 6.6 M CsCl.

Mitochondrial DNA in yeast recombination and subsequent modification following mating between a Grande and a suppressive Petite

The fate of mitochondrial DNA, following mating between a grande and suppressive petite of Saccharomyces cerevisiae, has been followed for up to 60 generations. The buoyant density of the mitochondrial DNA was seen to change in a manner explicable by a combination of recombination and subsequent modification phenomena whilst the suppressivity of the petite zygotic clones always remained high. These findings are consistent with current models of mitochondrial DNA metabolism in which petite strains have been observed to undergo deletion and reamplification of certain parts of their genomes.