Repair mechanisms of UV-induced DNA damage in soybean chloroplasts

In order to better understand the biochemical mechanisms of DNA metabolism in chloroplasts, repair of UV induced plastome damage in vivo was determined by exposure of soybean suspension cells to UV light and subsequent quantitation of the damage remaining in nuclear and chloroplast encoded genes with time by quantitative polymerase chain reaction (QPCR). The kinetics of damage rapir in the nuclear rbcS gene suggest that photoreactivation and dark mechanisms are active, while for the plastome encoded psbA gene only a light-dependent repair process was detected which is considerably slower than would be expected for photolyase-mediated photoreactivation.     

Precedence of the first male sperm in successive matings in the HymenopteraDiadromus pulchellus

In most insect species where double matings occur, sperm from the second male preferentially fertilize subsequent eggs. However, we demonstrate here that, as already shown for some other hymenopteran species, this is not the case in the ichneumonid waspDiadromus pulchellus (Wesmeal): sperm from the first male usually father all the female progeny. This precedence of the first male sperm is also observed in double matings involving an haploid male and a diploid sterile male, whichever is the first mating male. We discuss the consequences of this phenomenon from an evolutionary point of view.     

Prolonged aerated hydration for improvement of seed quality in Brassica oleracea L.

Seeds of cauliflower cv. Hipop and Brussels sprouts cv. Asmer Aries were aged at 20% moisture content for 24 h; all seeds retained a germination of over 70% after ageing although the mean germination time increased. Prolonged aerated hydration for up to 32 h at 20°C followed drying resulted in improved performance of both unaged and aged cauliflower seeds and aged Brussels sprouts. Thus, all seed showed reductions in the mean germination time to the extent that after 32 h hydration the aged cauliflower seeds performed as well as high quality unaged seed. The improvement of aged seeds was also revealed an increase in germination after the controlled deterioration test following up to 24 h (cauliflower) or 32 h (Brussels sprouts) aerated hydration. This increase was indicative of a decrease in the extent of deterioration present after aerated hydration. Deleterious effects of prolonged hydration were observed in Brussels sprouts after 32 h although these may be explained desiccation injury after treatment since radicle emergence had occurred during hydration. The improvements in seed performance may be explained the activation of metabolic repair occurring during the early part of the hydration period therereducing the extent of deterioration that has been sustained during ageing, with further improvements due to the advancement of the germination process.     

Apoptosis in anititumor strategies: Modulation of cell cycle or differentiation

There is a strong evidence that administration of antitumor drugs triggers apoptotic death of target cells. A characteristic feature of appotosis is active participation of the affected cell in its demise. Attempts have been made, therefore, to potentiate the cytotoxicity of a variety of agents by modulating the propensity of cells to respond by apoptosis. Several strategies to enhance apoptosis that involve modulation of the cell cycle or differentiation are discussed. Loss of control of the G₁ checkpoint in tumor cells allows one to design treatments that arrest normal cells at the checkpoint and attempt to selectively kill tumor cells with S phase specific drugs. The possibility of a restoration of the apoptosis triggering function of the tumor suppressor gene p53 when the G₁ checkpoint function is abolished is expected to increase tumor cells' sensitivity to S phase poisons. Because induction of apoptosis by many antitumor drugs is cell cycle phase specific, drug combinations that preferentially trigger apoptosis at different phases of the cycle, or recruitment of cells to the sensitive phase, offer another antitumor strategy. There is also evidence that apoptosis is potentiated when cell differentiation is triggered follwing DNA damage. This observation suggests that strategies which combine DNA damaging and differentiating drugs, under conditions where the latter are administered following DNA damage caused by the former, may be successful.     

Crystallization of alpha 1-acid glycoprotein

A possible link between cellular cyclic AMP content and Na+K+ATPase activity was investigated in homogenates of rat kidney. Enzyme kinetics of Mg2+ and Na+K+ATPase were run in the presence of cyclic AMP, dibutyryl cAMP and compounds expected to elevate cyclic AMP levels such as forskolin, a potent adenylate cyclase activator, IBMX, an inhibitor of phosphodiesterases, and the beta-agonist isoproterenol. Medullary Na+K+ATPase is strongly inhibited by cyclic AMP whereas cortical Na+K+ATPase was stimulated in the same conditions. The correlation between ATPase activity and cellular cyclic AMP content supports the concept of a possible regulation of the enzyme by cyclic AMP.     

Further purification and characterization of human 3-methyladenine-DNA glycosylase Evidence for broad specificity

Further purification of a human placental 3-methyladenine-DNA glycosylase by phosphocellulose column chromatography yielded a 6000-fold increase in specific activity with greater than 5% recovery. Although 3-methyladenine was the predominant base released from double-stranded methylated DNA by this enzyme, minor releasing activities for 7-methylguanine and 3-methylguanine were also observed. During purification, the three DNA glycosylase activities consistently copurified with constant ratios of specific activity. Moreover, all the activities were heat-inactivated at 50°C at the same rate, required double-stranded methylated DNA as substrate, were inhibited by spermine and spermidine, and were not subject to product inhibition. These data strengthen the likelihood that the three activities are associated with a single DNA glycosylase.     

A cytochemical approach to the wound repair mechanism inUdotea petiolata (Siphonales)

Summary When injured, the thalli of the coenocytic algaUdotea petiolata undergo a rapid sealing process mainly due to the extrusion of two successive plugs. In the first, external and transitory plug, sulphated polysaccharides are the predominant components. In the second, permanent and internal plug, roundish bodies having a complex polysaccharidic composition are embedded in a fibrillar matrix of still unknown nature. The sulphated sugars were identified and located by means of Alcian Blue staining and X-ray microanalysis. A periodic acid-thiocarbohydrazide-silver proteinate technique proved useful especially in the study of the roundish bodies and in the compositional and structural comparison of the siphon wall with the wound wall. Phosphotungstic acid at low pH was used to evidentiate an extensive plasma membrane activity in the repairing cytoplasm.Supported by a grant of C.N.R.     

DNA sequence analysis of the defective interfering particles of bacteriophage f1.

Restriction mapping and nucleotide sequence analysis of several defective, interfering particles of bacteriophage f1 are described. These particles contain the nucleotide sequences corresponding to the carboxyl terminus of gene IV and the amino-terminus of gene II and the intergenic space between them. Tandem duplication of a portion of this intergenic space generates defective particles with novel nucleotide sequences not found in wild-type f1. This duplication is shown to contain the origin of complementary strand synthesis. Our results suggest that the duplication occurs at the site of gene II protein action, i.e. the origin of viral strand synthesis. A model is presented for the generation of these duplications in defective particles.     

聚多巴胺改性聚合物在神经修复中的研究进展 *

多巴胺在碱性条件下会发生自聚合生成聚多巴胺。由于聚多巴胺具有超强黏附性能,在过去几年中其被大量应用于修饰各类生物材料。神经修复中使用的材料多为聚合物,但单独使用聚合物修复神经的效果不佳。聚多巴胺改性聚合物的亲水性和生物相容性均优于单一聚合物。除此以外,聚合物上的聚多巴胺涂层还可用于进一步修饰促进神经修复的分子。综述了聚多巴胺的合成机理、性能以及聚多巴胺改性各类聚合物在神经修复中的研究进展,并展望了该类材料的发展前景。     

Restriction map of Chinese hamster mitochondrial DNA containing replication coordinates: comparison with Syrian hamster mitochondrial genome

A precise physical map, containing the structurally and operationally defined D-loop origin, terminal region, and direction of heavy-strand replication, has been constructed for mitochondrial DNA (mtDNA) from ovary (CHO-KI) and lung cells of Chinese hamster (Cricetulus griseus 2 N = 22), and compared with our previously established genome coordinates for mtDNA from Syrian hamster ( Mesocricetus auratus 2 N = 44). All four HpaI sites in Cricetulus are conserved in Mesocricetus (8 sites). Extensive variation exists for hexanucleotides cleaved by EcoRI HindIII PstI. KpnI and BamHI. Sequence divergence between Chinese and Syrian hamster mtDNAs, as reflected from analysis of the mapped recognition sites for these six endonucleases, is estimated as 5–9% base substitutions. mtDNAs from both hamster and several other mammalian species contain a commonly conserved HpaI site in the region of light strand initiation.