[Isolation of intact supercoiled mitochondrial DNA from the yeast Saccharomyces cerevisiae]. / Vydelenie intaktnoi kol'tsevoi superspiralizovannoi mitokhondrial'noí DNK drozhzheí-sakharomitsetov.

Cells of Saccharomyces cerevisiae strain PG-60 were mechanically disrupted in the presence of ethidium bromide, and the total covalently closed circular DNA (ccDNA) was prepared by EthBr-CsCl equilibrium centrifugation of lysed 15 g pellet of the homogenate. Recentrifugation of ccDNA in equilibrium neutral CsCl density gradient resolved a discrete light peak (LccDNA) with the buoyant density equal to 1.684 g/cm3 to about 10% of total ccDNA. Electron microscopy has shown that LccDNA contained circular molecules with the contour length around 25 micrometer circles and their multimeres. Well characterized linear mtDNA was transcribed with E. coli RNA-polymerase and cRNA obtained was hybridized with LccDNA 2 mu DNA and total DNA from yeast petit mutant, lacking mtDNA. Hybridization experiments have shown that the transcript of mtDNA hybridized almost exclusively with LccDNA. We have concluded that 25 micrometer circles of the LccDNA represent intact molecules of yeast mitochondrial DNA.

[Repair of mitochondrial DNA after x-ray irradiation of teleost fish loach Misgurnus fossillis eggs]. / Reparatsiia mitokhondrial'noi DNK posle rentgenovskogo oblucheniia iaitsekletok v'iuna Misgurnus fossilis.

X-ray irradiation of loach Misgurnus fossilis mature eggs induces breaks in mtDNA molecules with efficiency about 100 ev per break. The yield of damaged molecules of mtDNA reduces after fertilization or activation of irradiated eggs and subsequent incubation. Two-fold reduction in the relative amount of broken DNA molecules in mitochondria is observed after an 6-7 hour incubation. X-ray irradiation largely accelerates mtDNA synthesis in eggs. Activation of mtDNA synthesis is observed in whole irradiated eggs and in mitochondria isolated from them as well. Appearance of nascent DNA in the broken mtDNA molecules indicates the repair nature of mtDNA synthesis induced by X-irradiation.

[Density gradient ultracentrifugation method of studying sibiromycin interaction with linear and circular DNA]. / Issledovanie vzaimodeistviia sibiromitsina s lineinoi i kol'tsevoi DNK metodom ul'tratsentrifugirovaniia v gradientakh plotnosti.

Sibiromycin added to linear chromosomal E. coli DNA in vitro leads to the decrease of bouyant density in neutral CsCl density gradient. This decrease is a linear function of sibiromycin/DNA ratio and amounts to about 32 mg/ml at the ratio equal to 0.1. Binding sibiromycin does not change the degree of hydration of DNA as revealed by centrifugation in metrizamide density gradients. When added to the covalently closed or open circular DNA of PM-2 phage, sibiromycin decreased the bouyant density of these DNA species to a similiar extent. The antibiotic does not induce single-strand breaks in DNA in vitro as follows from the results of ethidium bromide-CsCl density gradient centrifugation of covalently closed PM-2 DNA.

[Simple procedure for the isolation of animal mitochondrial deoxyribonucleic acid]. / Prostaia metodika vydeleniia mitokhondrial'noi DNK iz zhivotnykh tkanei.

A simple procedure for the isolation of animal mitochondrial DNA is described. It includes deproteinization of mitochondrial lysates with phenol, precipitation of total nucleic acids with polyethylene glycol, RNA precipitation by saet and final purification of DNA using gel chromatography on a Sepharose 4B column. MtDNA preparations obtained were free from protein and RNA and were represented predimonantly by the covalently closed molecules. The content of D-looped molecules in these preparations was equal to 45%.

[Properties of the cell-free protein synthesizing system from the fibroin region of the Bombyx mori silkgland]. / Svoistva beskletochnoi sistemy belkovogo sinteza iz fibroinovogo otdela shelkootdelitel'noi zhelezy tutovogo shelkopriada Bomby x mori.

Microsomes isolated from the fibroin region of the Bombyx mori silkgland synthesize in the cell-free system a glycin rich polypeptide or polypeptides presumably representing fibroin precursors. Besides microsomes the system requires ATP and ATP-generating system, GTP, soluble protein fraction and tRNA, glycine incorporation is inhibited by puromycin and cycloheximide. It is shown that the synthesis of a polypeptide with high Gly/Lys ratio requires soluble protein fraction isolated from the silk gland at the end of the instar V. When the soluble protein fraction from the larvoe at the early instar V is used the Gly/Lys ratio in the product is markedly lower. These results permit to suggest that fibroin synthesis may be regulated at the level of tRNA aminoacylation.

RNA-polymerase activity in isolated nuclei of developing silkworm embryos.

Nuclei isolated from developing embryos of the silkworm (Bombyx mori) are capable of RNA synthesis in vitro. The incorporation of C-14-uridine triphosphate (C-14-UTP) into the acid-insoluble fraction requires the presence of the other three ribonucleoside triphosphates; it is inhibited by actinomycin, olivomycin, and ethidium bromide, and is stimulated by ammonium sulfate. In a medium of moderate ionic strength C-14-UTP incorporation is slightly inhibited by alpha-amanitine (4 mug/ml), whereas in the presence of 0.2 M ammonium sulfate the same alpha-amanitine concentration reduces the incorporation by 90%. These data indicate that silkworm embryo nuclei, like nuclei from several other sources, contain two different RNA-polymerase fractions.