The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA

Base ratios and total DNA amounts can vary substantially between and within higher taxa and genera, and even within species. Gene conversion is one of several mechanisms that could cause such changes. For base substitutions, disparity in conversion direction is accompanied by an equivalent disparity in base ratio at the heterozygous site. Disparity in the direction of gene conversion at meiosis is common and can be extreme. For transitions (which give purine [R]/pyrimidine [Y] mispairs) and for transversions giving unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow but systematic changes in G + C percentage. For transversions giving like R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the extent of correction direction disparity, one can deduce properties of repair enzymes, such as the ability (1) to excise preferentially the purine from one mispair and the pyrimidine from the other for two different R/Y mispairs from a single heterozygous site and (2) to excise one base preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show strong disparity in conversion direction, with preferential cutting of the nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA. The opposite directions of disparity for frame-shifts and their intragenic suppressors as Ascobolus suggest that repair enzymes have a strong, systematic bias as to which strand is cut. The conversion spectra of mutations induced with different mutagens suggest that the nonlooped strand is preferentially cut, so that base additions generally convert to mutant and deletions generally convert to wild-type forms. Especially in nonfunctional or noncoding DNA, this could cause a general increase in DNA amounts. Conversion disparity, selection, mutation, and other processes interact, affecting rates of change in base ratios and total DNA.      

Cryopreservation of immature spring wheat zygotic embryos using an abscisic acid pretreatment

Spring wheat (Triticum aestivum L.) zygotic embryos were successfully cryopreserved, without the addition of exogenous cryoprotectants, using only an abscisic acid (ABA) pretreatment. Optimum survival was obtained when embryos were cultured in vitro for 10 days on semisolid Murashige and Skoog (MS) nutrient medium supplemented with 0.5 mg/L (±) ABA prior to cryopreservation. The embryos resumed growth within three days when returned to MS medium devoid of ABA but containing 2mg/L 2,4-dichlorophenoxyacetic acid. The embryogenic calli produced from these embryos exhibited normal plant regeneration on auxin-free media. Changes in dw/fw ratio, as well as the esterified fatty acid and sucrose concentrations correlated positively with the development of tolerance to cryopreservation.NRCC Publication No. 33519     

Degradation of (+/-)-synephrine by Arthrobacter synephrinum. Oxidation of 3,4-dihydroxyphenylacetate to 2-hydroxy-5-carboxymethyl-muconate semialdehyde.

1. Cell-free extracts of Arthrobacter synephrinum catalyse the oxidation of 3,4-dihydroxy-phenylacetate. 2. The product of oxidation was characterized as 2-hydroxy-5-carboxymethylmuconate semialdehyde from its chemical behaviour as well as from nuclear-magnetic-resonance spectra. 3. A 3,4-dihydroxyphenylacetate 2,3-dioxygenase (EC 1.13.11.15) was partially purified from A. synephrinum. 4. The enzyme had a Km of 25 micrometer towards its substrate and exhibited typical Michaelis-Menten kinetics. 5. The enzyme also catalysed the oxidation of 3,4-dihydroxymandelate and 3,4-dihydroxyphenylpropionate, at reaction rates of 0.5 and 0.04 respectively of that for 3,4-dihydroxyphenylacetate. 6. The enzyme was sensitive to treatment with thiol-specific reagents. 7. The molecular weight of the enzyme as determined by Sephadex G-200 chromatography was approx. 282000.     

Microbial metabolism of phenolic amines: degradation of dl-synephrine by an unidentified arthrobacter.

Microorganisms capable of degrading dl-synephrine were isolated from soil of Citrus gardens by enrichment culture, with dl-synephrine as the sole source of carbon and nitrogen. An organism which appears to be an arthrobacter, but which cannot be identified with any of the presently recognized species was predominant in these isolates. It was found to metabolize synephrine by a pathway involving p-hydroxyphenylacetaldehyde, p-hydroxyphenylacetic acid, and 3,4-dihydroxyphenylacetic acid as intermediates. Some of the enzymes of this pathway were demonstrated in cell-free extracts. An aromatic oxygenase, which could also be readily obtained in a cell-free system, was found to degrade 3,4-dihydroxyphenylacetic acid by meta cleavage.     

Wound healing activity of NOE-aspirin: a pre-clinical study.

Aspirin, one of the oldest non-steroidal anti-inflammatory drugs, impedes tissue repair by virtue of retarding inflammation. The present study was undertaken to find out if linking of nitrooxyethyl ester to aspirin reverses its healing-depressant propensity. Nitrooxyethyl ester of aspirin (NOE-Asp) was synthesized in our laboratory through well-established synthetic pathway, starting from aspirin through esterification with ethylene glycol and nitration with a mixture of nitric and sulfuric acids at 0 degrees C. The effect of NOE-Asp on phases of healing such as collagenation, wound contraction and epithelialization and on scar size of healed wound was evaluated in three wound models-incision, dead space, and excision wounds. To assess its influence on the oxidative stress, the levels of glutathione (GSH) and thiobarbiturate reactive species (TBARS) were also determined in 10-day-old granulation tissue. NOE-Asp was further screened for its anti-inflammatory activity in rat paw edema model. NOE-Asp promoted collagenation (increase in breaking strength, granulation weight, and collagen content), wound contraction, and epithelialization phases of healing. NOE-Asp also showed a significant antioxidant effect in 10-day-old granulation tissue as compared to aspirin. The results vindicate our assumption that the esterification of aspirin with nirooxyethyl group reverses the healing-suppressant effect of aspirin. The compound also showed equipotent anti-inflammatory activity as aspirin.     

The phylogeny and evolution of host choice in the Hippoboscoidea (Diptera) as reconstructed using four molecular markers

Hippoboscoidea is a superfamily of Diptera that contains the Glossinidae or tsetse flies, the Hippoboscidae or louse flies, and two families of bat flies, the Streblidae and the Nycteribiidae. We reconstruct the phylogenetic relationships within Hippoboscoidea using maximum parsimony and Bayesian methods based on nucleotide sequences from fragments of four genes: nuclear 28S ribosomal DNA and the CPSase domain of CAD, and mitochondrial 16S rDNA and cytochrome oxidase I. We recover monophyly for most of the presently recognized groups within Hippoboscoidea including the superfamily as a whole, the Hippoboscidae, the Nycteribiidae, the bat flies, and the Pupipara (=Hippoboscidae+Nycteribiidae+Streblidae), as well as several subfamilies within the constituent families. Streblidae appear to be paraphyletic. Our phylogenetic hypothesis is well supported and decisive in that most competing topological hypotheses for the Hippoboscoidea require significantly longer trees. We confirm a single shift from a free-living fly to a blood-feeding ectoparasite of vertebrates and demonstrate that at least two host shifts from mammals to birds have occurred. Wings have been repeatedly lost, but never regained. The hippoboscoid ancestor also evolved adenotrophic viviparity and our cladogram is consistent with a gradual reduction in the motility of the deposited final instar larvae from active burrowing in the soil to true pupiparity where adult females glue the puparium within the confines of bat roosts.     

Identification and characterization of rad51 of Pneumocystis

Rad51, a eukaryotic homolog of RecA, is an important protein involved in DNA recombination and repair. We have characterized rad51 of Pneumocystis carinii and Pneumocystis murina. rad51 is a single copy gene that encodes a 1.2 kb mRNA, which contains an open reading frame encoding 343 amino acids. Rad51 from Pneumocystis showed high homology to those from yeast. ATP binding motifs GEFRTGKS and LLIVD, similar to those of Saccharomyces cerevisiae and Schizosaccharomyces pombe, are conserved in Pneumocystis Rad51. The recombinant protein when expressed in E. coli showed DNA-dependent ATPase activity. Since Rad51 is a key enzyme in DNA repair and recombination, it potentially plays an important role in the recombination process leading to antigenic variation and thereby resistance to host immune responses in Pneumocystis.