ATR and a Chk1-Aurora B pathway coordinate postmitotic genome surveillance with cytokinetic abscission

Aurora B regulates cytokinesis timing and plays a central role in the abscission checkpoint. Cellular events monitored by this checkpoint are beginning to be elucidated, yet signaling pathways upstream of Aurora B in this context remain poorly understood. Here we reveal a new connection between postmitotic genome surveillance and cytokinetic abscission. Underreplicated DNA lesions are known to be transmitted through mitosis and protected in newly formed nuclei by recruitment of 53BP1 and other proteins until repair takes place. We find that this genome surveillance initiates before completion of cytokinesis. Elevating replication stress increases this postmitotic process and delays cytokinetic abscission by keeping the abscission checkpoint active. We further find that ATR activity in midbody-stage cells links postmitotic genome surveillance to abscission timing and that Chk1 integrates this and other signals upstream of Aurora B to regulate when the final step in the physical separation of daughter cells occurs.     

Conformational analysis of an EP24.15 inhibitor by NMR and molecular modelling

The enzyme thimet oligopeptidase (EC3.4.24.15, EP24.15) is responsible for the hydrolysis of a number of neuropeptides. Despite much research examining its substrate specificity, little is known about the conformational requirements of its active site. We have used 1D ¹H and 2D TOCSY NMR experiments to assign the proton resonances of the EP24.15 inhibitor, N-[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Tyr-p-aminobenzoate (cFP), and 2D ROESY NMR to investigate whether cFP exhibits any conformational preferences in CD₃OD and in aqueous CD₃OD. Molecular modelling of charged cFP in the gaseous phase generated a number of conformations that were consistent with the NMR data obtained in CD₃OD. Analogous modelling on the uncharged cFP did not result in conformations consistent with any of the NMR data, but did suggest that, under non-polar conditions, cFP could adopt a hairpin conformation which would allow simultaneous coordination of the two carboxyl groups of cFP to the zinc ion in the active site of EP24.15.     

Influence of pastoral fallow on plant root growth and soil physical and chemical characteristics in a hill pasture

Pastoral fallowing over a growing season (October–May) has a profound effect on standing biomass and sward structure, and should have an impact on below ground plant growth and soil biological activities. Two field studies were conducted to compare the effects of pastoral fallow with rotational grazing on root growth and soil physical and chemical properties. Root growth and distribution was altered by pastoral fallowing and there was significantly (P < 0.01) less root biomass at 0–50 mm depth of soil in the fallowed sward than the grazed sward. Compared with the grazed treatment, pastoral fallow increased soil air permeability at 500 mm tension by 38%, saturated hydraulic conductivity by 26%, unsaturated hydraulic conductivity at 20 mm tension by 67% and soil moisture by 10–15%, and reduced soil bulk density by 11%. Fallowing had little effect on soil nutrients both at the end of fallowing, except for small reductions in K and Mineral N levels at 0–75 mm soil depth, and two to three years after fallowing.     

Molecular structure of exonuclease I from Escherichia coli B

Exonuclease I of Escherichia coli B (EC 3.1.4.25) was determined to be a monomeric protein of molecular weight approx. 72,000, as estimated by Sephadex gel filtration, sedimentation velocity centrifugation, and sodium dodecylsulfate polyacrylamide gel electrophoresis.