RecA-mediated cleavage reaction of Lambda repressor and DNA strand exchange require an active extended filament conformation but not ATP hydrolysis

DNA pairing and strand exchange activities are essential for genetic recombination. When DNA is damaged, RecA proteins bind to DNA in the presence of ATP and catalyze the specific proteolytic cleavage of Lambda repressor. The cleavage reaction induces and regulates the expression of DNA repair genes. In this work, it has been examined by introducing sites directed mutagenesis (in the ATP catalytic domain or in the DNA binding loop of RecA), the ability of RecA protein to hydrolyze ATP or tocleave Lambda repressor either in the presence of DNA or in the presence of high salt concentration, and the ability of RecA to promote DNA strand exchange. It was observed that mutant E96D does not hydrolyze ATP at all, but fulfills RecA functions such as cleavage of Lambda repressor and strand exchange in the presence of DNA. However mutant E158K hydrolyzes ATP as well in the presence of high salt concentration as in the presence of DNA, but does not fulfill RecA functions. These observations suggest that ATP hydrolysis is not required for the cleavage  of Lambda repressor and the genetic recombination, but is necessary for the release of RecA from DNA before DNA repair

Bacillus halodurans RecA-DNA binding and RecAmediated cleavage enhancing at alkaliphilic pH in vitro

In Escherichia coli, RecA protein catalyzes DNA pairing and strand exchange activities essential for genetic recombination. This is critical for normal cellular function under conditions that lead to alteredDNA metabolism and DNA damage. The RecA proteins of E. coli and Bacillus halodurans both can bind to DNA and catalyze the specific proteolytic cleavage of LexA and lambda repressor which inducesSOS response. At neutral pH self-cleavage of LexA depends exclusively on its binding to RecA filament, while at elevated pH (~10) it autodigests in the absence of RecA. We have shown in this work that the RecA-mediated cleavage and the binding of RecA to DNA promoted by B. halodurans are similar to those promoted by E. coli RecA, excepted that in the case of B. halodurans the rate of the cleavagereactions is increased at alkaline pH and that NaCl favors the binding of RecA to DNA. The results lead to two hypotheses for the pathway for RecA-mediated cleavage, in which we first suppose that theinternal pH of the bacteria is neutral. Thus LexA cannot undergo autodigestion, the genes involving in DNA repair and replication are not transcribed, regulating the growth of the cell. The second hypothesisis that the external environment and the internal pH of the bacteria are alkaline; here also the bacteria may have developed strategies to maintain LexA not inactivated. These observations suggest that theLexA autodigestion in B. halodurans at high pH may be regulated at the transcriptional level and that B. halodurans may be haloalkaliphile bacterium

DPPH antiradical scavenging, anthelmintic and phytochemical studies of Cissus poulnea rhizomes

peer reviewe

Bacteriophage Crosstalk: Coordination of Prophage Induction by Trans-Acting Antirepressors

Many species of bacteria harbor multiple prophages in their genomes. Prophages often carry genes that confer a selective advantage to the bacterium, typically during host colonization. Prophages can convert to infectious viruses through a process known as induction, which is relevant to the spread of bacterial virulence genes. The paradigm of prophage induction, as set by the phage Lambda model, sees the process initiated by the RecA-stimulated self-proteolysis of the phage repressor. Here we show that a large family of lambdoid prophages found in Salmonella genomes employs an alternative induction strategy. The repressors of these phages are not cleaved upon induction; rather, they are inactivated by the binding of small antirepressor proteins. Formation of the complex causes the repressor to dissociate from DNA. The antirepressor genes lie outside the immunity region and are under direct control of the LexA repressor, thus plugging prophage induction directly into the SOS response. GfoA and GfhA, the antirepressors of Salmonella prophages Gifsy-1 and Gifsy-3, each target both of these phages' repressors, GfoR and GfhR, even though the latter proteins recognize different operator sites and the two phages are heteroimmune. In contrast, the Gifsy-2 phage repressor, GtgR, is insensitive to GfoA and GfhA, but is inactivated by an antirepressor from the unrelated Fels-1 prophage (FsoA). This response is all the more surprising as FsoA is under the control of the Fels-1 repressor, not LexA, and plays no apparent role in Fels-1 induction, which occurs via a Lambda CI-like repressor cleavage mechanism. The ability of antirepressors to recognize non-cognate repressors allows coordination of induction of multiple prophages in polylysogenic strains. Identification of non-cleavable gfoR/gtgR homologues in a large variety of bacterial genomes (including most Escherichia coli genomes in the DNA database) suggests that antirepression-mediated induction is far more common than previously recognized

Effectiveness of binary combinations of Plectranthus glandulosus leaf powder and Hymenocardia acida wood ash against Sitophilus zeamais (Coleoptera: Curculionidae): Poster

Combinations of botanicals could enhance biological activity against insects. This in turn, will reduce amount of botanical used in storage protection. In this issue, the bioassay was carried out on Sitophilus zeamais to assess the effectiveness of binary combinations of Hymenocardia acida wood ash and Plectranthus glandulosus leaf powder regarding adult toxicity, progeny inhibition, and reduction of damage and germination ability. Plectranthus glandulosus leaf powder, H. acida wood ash and their binary combinations significantly induced mortality of S. zeamais adult (P? 0.0001). The higher mortality rate was achieved by the highest content (40 g/kg) of H. acida wood ash (94.66%) and 25PG75HA (94.59%) within 14 days of exposure. The combinations of P. glandulosus leaf powder with H. acida at different proportions produced different interactions. The combination made up by 75% of P. glandulosus leaf powder with 25% of H. acida wood ash produced synergistic effect whereas that made up by 50% of each of two powders had antagonistic effect in weevil mortality. The three combinations of H. acida and P. glandulosus significantly reduced the progeny production. In term of inhibition of F1, the combination 25PG75HA revealed more effective than the two other. The grain damage and population increase were significantly reduced. In general, the non-infested maize grain had a good germination rate than the infested ones. The treatments did not have negative effect on seed germination. From These results, the two powders and their binary combinations could be used to reduce grain infestation by insect while taking in account the proportions of insecticidal powders implied in the combination.Combinations of botanicals could enhance biological activity against insects. This in turn, will reduce amount of botanical used in storage protection. In this issue, the bioassay was carried out on Sitophilus zeamais to assess the effectiveness of binary combinations of Hymenocardia acida wood ash and Plectranthus glandulosus leaf powder regarding adult toxicity, progeny inhibition, and reduction of damage and germination ability. Plectranthus glandulosus leaf powder, H. acida wood ash and their binary combinations significantly induced mortality of S. zeamais adult (P? 0.0001). The higher mortality rate was achieved by the highest content (40 g/kg) of H. acida wood ash (94.66%) and 25PG75HA (94.59%) within 14 days of exposure. The combinations of P. glandulosus leaf powder with H. acida at different proportions produced different interactions. The combination made up by 75% of P. glandulosus leaf powder with 25% of H. acida wood ash produced synergistic effect whereas that made up by 50% of each of two powders had antagonistic effect in weevil mortality. The three combinations of H. acida and P. glandulosus significantly reduced the progeny production. In term of inhibition of F1, the combination 25PG75HA revealed more effective than the two other. The grain damage and population increase were significantly reduced. In general, the non-infested maize grain had a good germination rate than the infested ones. The treatments did not have negative effect on seed germination. From These results, the two powders and their binary combinations could be used to reduce grain infestation by insect while taking in account the proportions of insecticidal powders implied in the combination

Anthelmintic activity of phenolic acids from the axlewood tree<i>Anogeissus leiocarpus</i>on the filarial nematode<i>Onchocerca ochengi</i>and drug-resistant strains of the free-living nematode<i>Caenorhabditis elegans</i>

AbstractThe effect of three phenols (ellagic, gentisic and gallic acids) from the axlewood treeAnogeissus leiocarpusonOnchocerca ochengiand drug-resistant strains ofCaenorhabditis elegans, a model organism for research on nematode parasites, is investigated. Worms were incubated in different concentrations of phenols and their survival was monitored after 48 h. Among the three acids, ellagic acid strongly affected the survival ofO. ochengimicrofilariae,O. ochengiadults, a wild-typeC. elegansand anthelmintic-resistant strains ofC. elegans, namely albendazole (CB3474), levamisole (CB211, ZZ16) and ivermectin (VC722, DA1316), with LC50values ranging from 0.03 mmto 0.96 mm. These results indicate that the binding of ellagic acid in the worm differs from that of resistant strains ofC. elegans. The efficacy of both gallic and gentisic acids was not significantly changed in resistant strains ofC. eleganstreated with levamisole (ZZ16, LC50= 9.98 mm, with gallic acid), albendazole (CB3474, LC50= 7.81 mm, with gentisic acid) and ivermectin (DA1316, LC50= 10.62 mm, with gentisic acid). The efficacy of these three pure compounds is in accordance with the use ofA. leiocarpusfrom its locality of origin. Thein vivotoxicity data reveal that the thresholds are up to 200 times higher than the determined LC50values. Thus, ellagic acid could be a potential option for the treatment of nematode infections, even in cases of drug resistance towards established anthelmintic drugs.</jats:p

Immune recognition of<i>Onchocerca volvulus</i>proteins in the human host and animal models of onchocerciasis

AbstractOnchocerca volvulusis a tissue-dwelling, vector-borne nematode parasite of humans and is the causative agent of onchocerciasis or river blindness. Natural infections of BALB/c mice withLitomosoides sigmodontisand of cattle withOnchocerca ochengiwere used as models to study the immune responses toO. volvulus-derived recombinant proteins (OvALT-2,OvNLT-1,Ov103 andOv7). The humoral immune response ofO. volvulus-infected humans againstOvALT-2,OvNLT-1 andOv7 revealed pronounced immunoglobulin G (IgG) titres which were, however, significantly lower than against the lysate ofO. volvulusadult female worms. Sera derived from patients displaying the hyperreactive form of onchocerciasis showed a uniform trend of higher IgG reactivity both to the single proteins and theO. volvuluslysate. Sera derived fromL. sigmodontis-infected mice and from calves exposed toO. ochengitransmission in a hyperendemic area also contained IgM and IgG1 specific forO. volvulus-derived recombinant proteins. These results strongly suggest thatL. sigmodontis-specific andO. ochengi-specific immunoglobulins elicited during natural infection of mice and cattle cross-reacted withO. volvulus-derived recombinant antigens. MonitoringO. ochengi-infected calves over a 26-month period, provided a comprehensive kinetic of the humoral response to infection that was strictly correlated with parasite load and occurrence of microfilariae.</jats:p