Topoisomerase IV (topo IV), an essential factor during chromosome segregation, resolves the catenated chromosomes at the end of each replication cycle. How the decatenating activity of the topo IV is regulated during the early stages of the chromosome cycle despite being in continuous association with the chromosome remains poorly understood. Here we report a novel cell cycle-regulated protein in Caulobacter crescentus, NstA (negative switch for topo IV decatenation activity), that inhibits the decatenation activity of the topo IV during early stages of the cell cycle. We demonstrate that in C. crescentus, NstA acts by binding to the ParC DNA-binding subunit of topo IV. Most importantly, we uncover a dynamic oscillation of the intracellular redox state during the cell cycle, which correlates with and controls NstA activity. Thus, we propose that predetermined dynamic intracellular redox fluctuations may act as a global regulatory switch to control cellular development and cell cycle progression and may help retain pathogens in a suitable cell cycle state when encountering redox stress from the host immune response.
Cell fate determination in the asymmetric bacterium Caulobacter crescentus (Caulobacter) is triggered by the localization of the developmental regulator SpmX to the old (stalked) cell pole during the G1→S transition. Although SpmX is required to localize and activate the cell fate-determining kinase DivJ at the stalked pole in Caulobacter, in cousins such as Asticcacaulis, SpmX directs organelle (stalk) positioning and possibly other functions. We define the conserved σ 54 -dependent transcriptional activator TacA as a global regulator in Caulobacter whose activation by phosphorylation is indirectly down-regulated by SpmX. Using a combination of forward genetics and cytological screening, we uncover a previously uncharacterized and polarized component (SpmY) of the TacA phosphorylation control system, and we show that SpmY function and localization are conserved. Thus, SpmX organizes a site-specific, ancestral, and multifunctional regulatory hub integrating the in-phase oscillation of two global transcriptional regulators, CtrA (the master cell cycle transcriptional regulator A) and TacA, that perform important cell cycle functions.cell cycle | Caulobacter crescentus | σ 54 | SpmX | α-proteobacteria
The aim of the study was to evaluate the phytochemical components and antioxidant potential of methanolic and hydrophilic extracts isolated from in vivo and in vitro cultures of onion varieties of Bellary and CO 3. Phytochemical components like total flavonoids, phenolics, ascorbic acid and anthocyanins were analyzed. The antioxidant activities were examined by DPPH and FRAP methods. The results indicated that the both the methanolic extracts exhibited radical scavenging activity. The DPPH scavenging activity in Bellary and CO 3 onion varieties ranged from 6.5% -11.8% whereas FRAP values ranged from 0.9 -3.3 µM/100 µg FW. The total anthocyanins ranged from 9.9 -29.9 mg/kg, vitamin-C 48.6 -78.6 mg/kg, total phenolics and flavonoids content was 15.7 -34.7 mg/g GAE and 0.65 -1.17 mg/g respectively. Substantial amounts of anthocyanins, phenols, flavonoids and ascorbic acid were noticed in both the varieties. Our study revealed that the possible mechanism of the biological activities in onion could be due to the free radical scavenging and antioxidant activities. The polyphenols present in the onion bulbs may be responsible for these beneficial activities. This study clearly demonstrated that both the onion varieties possess very characteristic antioxidant potential that will help us in keeping good health.
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