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.      

cDNA cloning of a developmentally regulated hemocyanin subunit in the crustacean Cancer magister and phylogenetic analysis of the hemocyanin gene family

The complete cDNA sequence and protein reading frame of a developmentally regulated hemocyanin subunit in the Dungeness crab (Cancer magister) is presented. The protein sequence is aligned with 18 potentially homologous hemocyanin-type proteins displaying apparent sequence similarities. Functional domains are identified, and a comparison of predicted hydrophilicities, surface probabilities, and regional backbone flexibilities provides evidence for a remarkable degree of structural conservation among the proteins surveyed. Parsimony analysis of the protein sequence alignment identifies four monophyletic groups on the arthropodan branch of the hemocyanin gene tree: crustacean hemocyanins, insect hexamerins, chelicerate hemocyanins, and arthropodan prophenoloxidases. They form a monophyletic group relative to molluscan hemocyanins and nonarthropodan tyrosinases. Arthropodan prophenoloxidases, although functionally similar to tyrosinases, appear to belong to the arthropodan hexamer- type hemolymph proteins as opposed to molluscan hemocyanins and tyrosinases.      

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.     

Changes induced by sarcolysine in vivo in the composition of DNA-bound lipids in sarcoma 37

The two DNA fractions were isolated from sarcoma 37 by the use of the phenol method: supramolecular complex of DNA (SC DNA, 60%) and "phenol" nuclear matrix DNA (PNM DNA, 40%). The lipids in SC DNA represented of light and tightly bound components, the latter was similar to the lipid composition of PNM DNA. SC DNA contains 20 micrograms of neutral lipids (NL) and 6.5 micrograms of phospholipids (PL), while PNM DNA contains 9.8 micrograms of NL and 3.5 micrograms of PL per mg DNA. SC DNA-bound lipids of sarcoma 37 are deficient in free cholesterol (FC, 13%), but rich in cholesterol esters (CE, 39%) and free fatty acids (FFA, 23%); very rich in cardiolipin (CL, 43%) and phosphatidylethanolamine (PE, 28%), but deficient in phosphatidylcholine (PC, 12%). The tumor contains triglycerides (TG) that is absent in DNA of the normal cells. The injection of sarcolysine (10 micrograms/kg) markedly increased (1.5-3 times) the content of all LN and PL fractions in SC DNA, which was accompanied by both the accumulation of FC, TG, PC and the reduction of the remaining lipid fractions in PNM DNA. It is supposed, that DNA-bound lipids may be the target for the action of sarcolysine.     

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.