Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs

Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA is unusually variable among lepidosaurian reptiles. Phylogenetic and comparative analyses of cysteine tRNA gene sequences identify eight parallel losses of the D-stem, resulting in D-arm replacement loops. Sampling within the monophyletic Acrodonta provides no evidence for reversal. Slipped-strand mispairing of noncontiguous repeated sequences during replication or direct replication slippage can explain repeats observed within cysteine tRNAs that contain a D-arm replacement loop. These two mechanisms involving replication slippage can account for the loss of the cysteine tRNA D-stem in several lepidosaurian lineages, and may represent general mechanisms by which the secondary structures of mitochondrial tRNAs are altered.      

Radioprotective action of a GGS-10 gaseous hypoxic mixture on the DNA supramolecular complex of normal tissues and sarcoma 45 of rats

Gas hypoxic mixture (GHM-10) inhaled by rats during gamma-irradiation (2 to 20 Gy) effectively protects the supramolecular complex of DNA (SC DNA) in bone marrow and spleen, but fails to protect this complex in sarcoma 45. GHM-10 itself has been shown to induce rapid and prolonged, but irreversible, decrease in SC DNA elastic viscosity in normal tissues.     

Effect of choline on the DNA supramolecular complex in rats and their survival following gamma irradiation

The injection of choline-chloride (200 mg/kg) to rats 15 min before 6 Gy irradiation was shown to increase their survival rate over a period of 30 days, to prolong their average life, and to promote the complete restoration of elastoviscosity of DNA supramolecular complexes in thymus, spleen, liver and brain. When administered immediately after irradiation the drug increased the survival rate of rats.     

Thiol-induced fragmentation of chromosomal DNA]

Supramolecular complexes of DNA (SC DNA) were isolated from loach sperm, loach erythrocytes and hen erythrocytes by the phenol method. By the use of UV-sedimentation on neutral 5-20% sucrose gradient, we studied the effect of 2-mercaptoethanol (ME), dithiothreitol (DTT) and NaBH4 on SC DNA at different pH and long-time incubation (5 and 10 days). It appeared that ME treatment at pH 4.4 fragmented SC DNA of three objects into subunits of size 5 x 10(5)D. Incubation with DTT at pH 8 in the presence of EDTA resulted in subunits of size 1-2 x 10(7)D. However, NaBH4 at pH 8 failed to induce fragmentation of SC DNA. It is shown that ME-induced at pH 4.4 fragmentation is accompanied by a decrease in hyperchromatic effect of subunits, indicating the presence of "sticky" ends. Thus, ME-induced fragmentation of SC DNA results from a "clayting" double-strand break, involving, on an average, 180 bp.     

DNA-bound lipids from eukaryotic (loach spermatozoa, pigeon erythrocytes) and prokaryotic (E. coli B, phage T2) cells

Using thin-layer chromatography, some specific DNA-bound neutral lipids and phospholipids of loach spermatozoa, pigeon erythrocytes, E. coli B and phage T2 cells were studied. These lipids are represented by loosely and firmly bound components. The content of neutral lipids in the above DNAs (per mg of DNA) is 10.6, 4.8, 7.81 and 1.43 micrograms, respectively; that of phospholipids is 4.31, 1.28, 1.14 and 0.54 micrograms, respectively. The eucaryotic DNA-bound lipids are highly deficient of free cholesterol, phosphatidylcholine, phosphatidylinositol and phosphatidylserine but are rich in cardiolipin, phosphatidylethanolamine, cholesterol esters, diglycerides and free fatty acids. The quantitative and qualitative composition of DNA-bound lipids of loach spermatozoa changes during the transition from the superhelical to the relaxed conformation of DNA. Procaryotic DNA-bound neutral lipids are also represented by the free cholesterol, diglyceride and free fatty acid fractions, whereas the DNA-bound phospholipids of procaryotes consist of only two fractions, i.e., cardiolipin and phosphatidylethanolamine. The role of DNA-bound lipids in the structural and functional organization of eucaryotic and procaryotic genomes is discussed.     

Relation between the supercoiling of DNA from loach sperm and the environmental temperature

The effect of environmental temperature changes in the physiological range on DNA supercoiling in the sperm of Misgurnus fossilis L. was studied. Living fishes from the Oka and the Danube and isolated gonads were exposed to temperature changes. In the living fishes, both temperature increase from 4 to 14 degrees C and decrease from 19-21 to 14 degrees resulted in a reversible relaxation of DNA superhelices. Upon decreasing the environmental temperature from 19-21 to 4 degrees C the reversibility of changes in DNA supercoiling was not observed during the next 15 days. In isolated gonads the temperature increase from 4 to 14 degrees C had no effect on the sperm DNA supercoiling. The temperature-dependent changes in the sperm DNA supercoiling were not dependent on the loach population. It is assumed that the effect of changes in environmental temperature on the supercoiling of sperm DNA in vivo plays an important role in the activation of the genome after fertilization.