Cooperation of mitochondrial and nuclear genes specifying the mitochondrial genetic apparatus in Neurospora crassa

Nucleo-cytoplasmic interactions in the regulation of thymidine phosphorylation in Acetabularia

The activity of dT kinase (EC. 2. 7. 1. 75) was estimated during the development of nucleate and anucleate cells inAcetabularia. Enzyme activity increases as the cap attains its maximum diameter (Bannwarth & Schweiger 1975). Regulation of the dT kinase activity is observed even in the absence of the cell nucleus. Twelve to fifteen days after enucleation dT kinase activity increase sharply as the cap reaches its maximum diameter and decreases 5 days later. The increase is inhibited by puromycin, chloramphenicol, rifampicin and ethidium bromide but not by cycloheximide. These findings indicate that protein synthesis on 70S organelle ribosomes is involved in the regulation of the dT kinase. Since activities of mixtures from low activity cell extracts and from high activity cell extracts are additive, it is concluded that the regulation is not mediated through an activator protein but rather throughde novosynthesis of the enzyme protein.

Effects of cycloheximide and chloramphenicol on the synthesis of polypeptides found in three subcellular fractions of maize scutellum

The effects of two protein synthesis inhibitors, cycloheximide and chloramphenicol, on the synthesis of mitochondrial proteins in maize (Zea mays) have been studied. The results of these investigations suggest that while most of the mitochondrial proteins are synthesized in the cytoplasm and are subsequently associated with the mitochondrion, several proteins of the mitochondrial inner membrane are synthesized within the mitochondrion. These results are consistent with those observed in several other systems, but not previously reported for higher plants.

Proposed involvement of an internal promoter in regulation and synthesis of mitochondrial and cytoplasmic leucyl-tRNA synthetases of Neurospora

Genetic analysis of an electrophoretic variant of the mitochondrial leucyl-tRNA synthetase [L-leucine:tRNALeu ligase (AMP-forming), EC 6.1.1.4] indicates that it is either an allele of or linked closely to leu-5ts, a mutant that is known to produce a cytoplasmic leucyl-tRNA synthetase with an altered affinity for leucine as well as being deficient in the production of the mitochondrial enzyme. Immunological analysis indicates that the two synthetases have little, if any, structural homology. The pattern of synthesis of the enzymes in leu-5ts revertants, the reciprocal relationship of the production of the two enzymes in response to a negative regulatory element, presumably of mitochondrial origin, as well as the lack of detectable structural homology, led to the proposal that the phenotype of leu-5ts results from a mutational alteration in the structural gene for the cytoplasmic enzyme in a region involved in the initiation of transcription of the adjacent gene for the mitochondrial enzyme.

The genetic system of kinetoplasts in trypanosomatides

In the present report, the genetic system of Crithidia oncopelti kinetoplast is used as a model for investigation of kinetoplast DNA (kDNA) structure, its transcription, protein synthesizing apparatus of the kinetoplast and the protein synthesis controlled genetically by kDNA. It was shown that kDNA of C. oncopelti can be isolated from cells or from kinetoplast fraction in the form of a network complex structure consisting of a lot of circular molecules. These minicircles have a contour length of about 0.83 micronm and molecular weight of 1.6 X 10(6). The kDNA was demonstrated to be of higher AT content type than nuclear DNA. Besides, kDNA is characterized by a lesser degree of clustering of pyrimidines as compared with the nuclear one. The isolated kinetoplasts of C. oncopelti were shown to exhibit activity of DNA dependent RNA polymerase. The effect of some antibiotics and intercalating substances on RNA synthesis in kinetoplasts and mitochondria appears to be identical. Kinetoplasts of C. oncopelti have their own protein synthesizing system, whose components (ribosomes, rRNA, proteins, factors of incorporation) differ from those of the cytoplasm. Inhibition of translation by some antibiotics and of transcription by acriflavin allowed the suggestion that several proteins of kinetoplast ribosomes may be synthesized within this organoid. It was shown then that kDNA may be involved in the formation of the protein synthesizing apparatus in the kinetoplast.

Genetic control of mitochondrial malate dehydrogenases: evidence for duplicated chromosome segments

The genetic control of the major mitochondrial isoenzymes of malate dehydrogenase (L-malate:NAD+ oxidoreductase; EC 1.1.1.37) has been investigated in Zea mays. The mitochondrial isozymes are coded at four nuclear gene loci. Two of the loci (mdh1 and mdh2) are diallelic and tightly linked. The other two loci (mdh3 and mdh4) appear to have arisen by duplication of the chromosome segment carrying mdh1 and mdh2, but are not linked to them. The segregation of such a duplicate segment can explain anomalous backcross and F2 segregation ratios.

Regulation of cyanide-insensitive respiration in Neurospora

1. Inhibition of either mitochondrial transcription or translation in Neurospora crassa results in the rapid production of the cyanide-insensitive pathway of mitochondrial respiration. Protein synthesis on cytoplasmic ribosomes is required for the appearance of cyanide-insensitive respiration in the culture. 2. Removal of the inhibition of transcription of translation results in a rapid return to cyanide-sensitive respiration. Additional protein synthesis in the cytoplasm is required for the loss of cyanide-insensitive respiratory activity while additional mitochondrial protein synthesis has no effect. 3. These studies indicate that a mitochondrial gene product is involved in a negative manner in the regulation of cyanide-insensitive respiration. When the mitochondrial product is present, the pathway is not expressed, when the mitochondrial product is absent, the pathway is expressed. 4. Studies with forced heterokaryons formed from respiratory-deficient mutants having cyanide-insensitive respiration and respiratory-competent auxotrophs indicate that the site of action of the mitochondrial gene product is external to the mitochondrion.

Polypeptide binding to plastid envelopes during chloroplast development

Pulse-chase experiments using [(35)S]methionine with various light and dark regimes have been used to follow in situ polypeptide accumulation during plastid development in Avena sativa (var. Mostyn). Subsequent isolation and later fraction of the etioplasts, etio-chloroplasts or chloroplasts into envelope, stroma lamellae, thylakoid and supernatant (stromal) fractions has enabled a survey of the movement of label between the different fractions. These studies show that considerable and sometimes quite rapid plastidic protein interchange takes place even in the unilluminated etiolated tissue but this increases markedly as greening commences and that the synthesis and transport of polypeptides required for thylakoid assembly is a light-dependent process. Labelled polypeptides from each fraction were resolved by SDS-polyacrylamide gel electrophoresis, sectioned and counted. The well-washed envelope fractions contained several labelled polypeptides, one of which had an estimated molecular weight of 13,500 daltons. Upon subsequent tryptic digest of this envelope material and finger-printing by high voltage electrophoresis and paper chromatography, the distribution of 9 of the tryptic peptides was similar to that of tryptic peptides derived from authentic small sub-unit of Fraction I protein from Avena. This apparent attachment of the small sub-unit of Fraction I protein to the envelope may be part of the mechanism of transport of this protein from the cytoplasm to the stroma of the developing plastid.

Tertiary structure and function of closed-circular mitochondrial DNA and its transcription in vivo

The conformation of the closed circular mitochondrial DNA in cultured human cells is changed by the addition of berenil to the culture medium in such a way that the 34-S mitochondrial DNA is converted into a 29-S DNA and finally into a 24-S DNA. The superhelix density of the covalently closed 29-S mitochondrial DNA is sigma O = -1.5 times 10(-2) (turns/10 base pairs) and consequently is intermediate between the superhelix density of the 34-S DNA (sigma0 = -2.8 times 10(-2)) and that of the closed circular 24-S DNA (sigmao appromiately 0). Removal of the drug reverses the transition, covalently closed circular 34-S DNA to covalently closed circular 29-S DNA to covalently closed circular 24-S DNA. The covalently closed circular 24-S mitochondrial DNA is not replicated. Transcription of this DNA is also inhibited as indicated by the fact that no synthesis of the mitochondrial ribosomal RNAs occurs as long as the mitochondrial DNA is in this conformation. The covalently closed circular 29-S mitochondrial DNA is replicated but not transcribed in vivo.

Derepression in Saccharomyces cerevisiae can be dissociated from cellular proliferation and deoxyribonucleic acid synthesis

A method has been developed that permits precise control of release from catabolite repression in Saccharomyces cerevisiae. It consists of transferring cells growing exponentially on 5% glucose to derepression medium at high cell density. Derepression then proceeds with reproducible kinetics and is complete within 6 to 7.5 h for various intra- and extramitochondrial markers, in the absence of any substantial increase in cellular dry weight or protein. Nuclear (and mitochondrial) deoxyribonucleic acid synthesis can be interrupted in certain thermosensitive (cdc) mutants at the nonpermissive temperature; a shift to this temperature before the onset of derepression has no effect on its outcome.

Macromolecular enzymatic product of NAD+ in liver mitochondria

Rat liver mitochondria contain a Mg2+-requiring system that transfers the ADP-ribose moiety of NAD+ to an acceptor protein. The enzyme system was extracted in a soluble form and the ADP-ribosylated protein product was isolated by hydroxyapatite and Sephadex chromatography. The ADP-ribosylated protein product has a molecular weight of 100,000 and can be dissociated into subunits of 50,000 daltons by sodium dodecyl sulfate gel electrophoresis. Incubation of the isotopically labeled ADP-ribosylated protein with nicotinamide and a mitochondrial extract yields labeled NAD+, indicating apparent reversibility of the reaction. Enzymatic degradation of the ADP-ribosylated protein with snake venom phosphodiesterase liberates AMP and ADP-ribose or its isomer. Identification of these products and reversibility of the reaction show that the ADP-ribose moiety of NAD+ is the molecular species that is transferred to the acceptor protein. A fraction of the protein-bound ADP-ribose appears to be present as an an oligomer. The enzymatic protein-ADP-ribosylating reaction is inhibited by nicotinamide, ADP-ribose, the fluorophosphate of AMP, and picrylsulfonic acid.

Regulation of nuclear DNA replication by thechloroplast in Chlamydomonas

The experiments described in this paper implicate chloroplast protein synthesis in the regulation of nuclear DNA replication. The inhibition of nuclear DNA replication in the lower eukaryote, Chlamydomonas reinhardi strain 21gr, was examined after growth of cells with a series of antibiotics (streptomycin, neamine, spectinomycin, cleocin, chloramphenicol, and rifampicin) each of which has a known effect upon chloroplast RNA or protein synthesis in this organism. Each antibiotic inhibited nuclear DNA replication at drug concentrations at which there was little or no inhibition of adenine incorporation into chloroplast DNA. That chloroplast DNA was replicating under these conditions rather than merely being repaired, was shown first by the high incorporation rates and second by a (14)N-(15)N density transfer experiment in which chloroplast DNA doubled in the presence of streptomycin, while no incorporation into nuclear DNA was detected. A small DNA peak, Component III, located between nuclear and chloroplast DNA's in CsCl gradients, possibly mitochondrial, was more pronounced in DNA from antibiotic-inhibited cultures than from controls.

Accumulation of replicative intermediates of mitochondrial DNA in Tetrahymena pyriformis grown in ethidium bromide

The effect of growth of Tetrahymena pyriformis in ethidium bromide (EthBr) on the structure and synthesis of mitochondrial DNA (mtDNA) has been investigated. During the first 5 h of growth in EthBr, mtDNA synthesis is inhibited 95% or more. After 10-15 h, this block is partially released and large numbers of replicating molecules accumulate, indicating that inhibition by EthBr primarily affects the rate of chain growth and not the initiation of new rounds of replication. The accumulated molecules sediment more rapidly than normal Tetrahymena mtDNA and do not contain enough single-strand regions to distinguish them from normal Tetrahymena mtDNA when banded in buoyant CsCl or NaI gradients. Electron microscopy shows that the predominant species in this rapidly sedimenting DNA is a linear molecule containing one symmetrical double-stranded replication loop of varying size located at its center. No degradation of mtDNA from cells grown in EthBr was detected in alkaline velocity gradients.

Biochemical Studies on Development of Mitochondria in Pea Cotyledons during the Early Stage of Germination: Effects of Antibiotics on the Development

l-Leucine-U-(14)C was incorporated into mitochondrial protein in pea (Pisum sativum var. Alaska) cotyledons during the imbibing stages. Incorporation was almost completely inhibited by cycloheximide but not by chloramphenicol. Both antibiotics did not affect increases in mitochondrial activities and components of the cotyledons during imbibition. Therefore, mitochondrial development seems to be achieved by a transfer of protein pre-existing in the cytoplasm into the mitochondria rather than by de novo synthesis of mitochondrial protein. Cycloheximide stimulated an increase in bile saltsoluble protein of mitochondria in imbibing pea cotyledons. The recovery of cytochrome oxidase activity after sucrose density gradient centrifugation was enhanced, and the morphological properties of mitochondria were altered by cycloheximide.