Arg tyrosine kinase is involved in homologous recombinational DNA repair

c-Abl plays important roles in cellular response to DNA damage. However, possible roles for Arg (Abl-related gene) in DNA damage response are unknown. Here, we show that ionizing radiation (IR)-induced Rad51 focus formation is reduced in Arg-deficient cells generated from a chicken B cell line by targeted disruption. This is consistent with the findings that Arg-deficient cells display hypersensitivity to IR, elevated frequencies of IR-induced chromosomal aberrations, and reduced targeted integration frequencies. All of these abnormalities in DNA damage repair are also observed in ATM-deficient cells but not in c-Abl-deficient cells. Finally, we show that Arg interacts with and phosphorylates Rad51 in 293T cells. These results suggest that Arg plays a role in homologous recombinational (HR) DNA repair by phosphorylating Rad51.     

Differential protection by nitroxides and hydroxylamines to radiation-induced and metal ion-catalyzed oxidative damage

Modulation of radiation- and metal ion-catalyzed oxidative-induced damage using plasmid DNA, genomic DNA, and cell survival, by three nitroxides and their corresponding hydroxylamines, were examined. The antioxidant property of each compound was independently determined by reacting supercoiled DNA with copper II/1,10-phenanthroline complex fueled by the products of hypoxanthine/xanthine oxidase (HX/XO) and noting the protective effect as assessed by agarose gel electrophoresis. The nitroxides and their corresponding hydroxylamines protected approximately to the same degree (33-47% relaxed form) when compared to 76.7% relaxed form in the absence of protectors. Likewise, protection by both the nitroxide and corresponding hydroxylamine were observed for Chinese hamster V79 cells exposed to hydrogen peroxide. In contrast, when plasmid DNA damage was induced by ionizing radiation (100 Gy), only nitroxides (10 mM) provide protection (32.4-38.5% relaxed form) when compared to radiation alone or in the presence of hydroxylamines (10 mM) (79.8% relaxed form). Nitroxide protection was concentration dependent. Radiation cell survival studies and DNA double-strand break (DBS) assessment (pulse field electrophoresis) showed that only the nitroxide protected or prevented damage, respectively. Collectively, the results show that nitroxides and hydroxylamines protect equally against the damage mediated by oxidants generated by the metal ion-catalyzed Haber-Weiss reaction, but only nitroxides protect against radiation damage, suggesting that nitroxides may more readily react with intermediate radical species produced by radiation than hydroxylamines.     

Determination of the NMR structure of Gln25-ribonuclease T1

Ribonuclease (RNase) T1 is a guanyloribonuclease, having two isozymes in nature, Gln25- and Lys25-RNase T1. Between these two isozymes, there is no difference in catalytic activity and three-dimensional structure; however, Lys25-RNase T1 is slightly more stable than Gln25-RNase T1. Recently, it has been suggested that the existence of a salt bridge between Lys25 and Asp29/Glu31 in Lys25-RNase T1 contributes to the stability. To elucidate the effects of the replacement of Lys25 with a Gln on the conformation and microenvironments of RNase T1 in detail, the three-dimensional solution structure of Gln25-RNase T1 was determined by simulated-annealing calculations. As a result, the topology of the overall folding was shown to be very similar to that of the Lys25-isozyme except for some differences. In particular, there were two differences in the property of torsion angles of the two disulfide bonds and the conformations of the residues 11-13, 63-66, and 92-93. With regard to the residues 11-13, the lack of the above-mentioned salt bridge in Gln25-RNase T1 was thought to induce the conformational difference of this segment as compared with the Lys25-isozyme. Furthermore, it was proposed that the perturbation of this segment might transfer to the residues 92-93 via the two disulfide bonds.     

Individuals exhibiting conspicuous nevi (lentigo simplex) are resistant to allergic rhinitis/conjunctivitis (pollinosis), but those who do not show increased susceptibility to pollinosis

We investigated 115 individuals in Tokyo from two groups of persons with conspicuous nevi on the head, neck, and arms, etc. (nevus-positive group) and persons who do not exhibit such nevi (nevi-negative group) interviewing them to determine whether they suffered from allergic rhinitis/conjunctivitis (pollinosis) and examining them for the presence and extent of nevi. There was a distinct correlation: only 5 persons among 85 individuals of the nevus-positive group suffered from pollinosis, and all 30 people in the nevus-negative group had pollinosis. Thus, individuals exhibiting conspicuous nevi are resistant to pollinosis, but those who do not show increased susceptibility to pollinosis.     

Period and phase adjustments of human circadian rhythms in the real world

Entrainment of the circadian rhythm has 2 aspects, period and phase adjustments, which are established simultaneously in most nonhuman circadian systems. The human circadian system is unique in its functional structure in which 2 different subsystems are involved; one is the circadian pacemaker analogous to that located in the suprachiasmatic nucleus, and the other is the oscillatory system of unknown nature that drives the rest-activity cycle. The human circadian system shows the endogenous period very close to 24 h under entrainment and less sensitive to photic stimuli than under free running, which may explain stable entrainment in the real word where natural sun lights are unpredictable in terms of the intensity and time of appearance. On the other hand, nonphotic entrainment seems to play a significant role in phase adjustment of the human circadian system. Nonphotic zeitgebers initially directed to the rest-activity cycle may affect the circadian pacemaker through feedback and/or associated LD cycles.     

Selective cleavage of 10-methyl benzo[b]naphtho[2,1-d]thiophene by recombinant Mycobacterium sp. strain

Recombinant Mycobacterium sp. strain MR65 carrying dszABCD genes was used for desulfurization of 10-methylbenzo[b]naphtho[2,1-d]thiophene (10-methyl BNT) in the hexadecane phase. The specific activity was 25% of that of dibenzothiophene (DBT). One of two major metabolites of 10-methyl BNT produced by strain MR65 was identified as 1-methoxy-2-(3-methylphenyl)naphthalene by ¹H and ¹³C NMR. The other major metabolite and two minor metabolites were determined as 1-hydroxy-2-(3-methylphenyl)naphthalene, 2-(2-methoxy-3-methylphenyl)naphthalene and 2-(2-hydroxy-3-methylphenyl)naphthalene, respectively, by HPLC and GC-MS. The production ratio of the two desulfurization metabolite isomers was 0.99:0.01, calculated on the basis of peak GC areas. These results indicated that the C-S bond adjacent to the naphthalene skeleton was selectively cleaved to form the two major compounds.     

Effect of ruthenium precursor on hydrogen-treated active carbon supported ruthenium catalysts for ammonia synthesis

Active carbon (A.C.), after treatment at 1123 K with hydrogen for more than 24 h, was found to be very effective as a support for ruthenium catalysis in ammonia synthesis. The activity of barium promoted Ru catalysts supported on this treated A.C. is affected remarkably by the Ru precursor. Ru₃(CO)₁₂ was found previously to be the most effective Ru precursor for oxide supports such as Al₂O₃, MgO, and CeO₂ in ammonia synthesis. However, in this study, the Ru---Bao/A.C. catalyst prepared from Ru(acac)₃ was found to yield the highest activity, while the catalyst prepared from Ru₃(CO)₁₂ resulted in the lowest activity among several precursors. Transmission electron microscopy and hydrogen chemisorption showed that the particle size of Ru obtained from the decomposition of Ru(acac)₃ on hydrogen-treated A.C. is smaller than the particle size of Ru obtained from the decomposition of Ru₃(CO)₁₂. Additionally, RuCl₃ was found to be an effective precursor for Ru/A.C. catalyst. It has been suggested that chlorine ions can be removed easily from A.C. by hydrogen reduction at 773 K, and that this results in the high activity.     

C-ABI3, the Carrot Homologue of the Arabidopsis ABI3, is Expressed during Both Zygotic and Somatic Embryogenesis and Functions in the Regulation of Embryo-Specific ABA-Inducible Genes

A carrot gene homologous to the ABI3 gene of Arabidopsis wasisolated from a carrot somatic embryo cDNA library and designatedC-ABI3. The sequence of C-ABI3 was very similar to those ofABI3 of Arabidopsis and VP1 of maize in certain conserved regions.The expression of C-ABI3 was detected specifically in embryogeniccells, somatic embryos and developing seeds. Thus, expressionof C-ABI3 was limited to tissues that acquired desiccation tolerancein response to endogenous or exogenous abscisic acid (ABA).Endogenous levels of ABA in seeds increased transiently andthen desiccation of seeds started. The expression of C-ABI3in developing seeds was observed prior to the increase in levelsof endogenous ABA that was followed by desiccation of seeds.In transgenic mature leaves in which C-ABI3 was ectopicallyexpressed, expression of ECP31, ECP63 and ECP40 was inducedby treatment with ABA, which indicates that the expression ofECP genes was controlled by the pathway(s) that involved C-ABI3and ABA. This suggests that C-ABI3 has the same function asVP1/ABI3 factor in carrot somatic embryos. (Received March 4, 1998; Accepted September 4, 1998)