Escherichia coli DNA Topoisomerase I and Suppression of Killing by Tn5 Transposase Overproduction: Topoisomerase I Modulates Tn5 Transposition

Tn5 transposase (Tnp) overproduction is lethal to Escherichia coli. The overproduction causes cell filamentation and abnormal chromosome segregation. Here we present three lines of evidence strongly suggesting that Tnp overproduction killing is due to titration of topoisomerase I. First, a suppressor mutation of transposase overproduction killing, stkD10, is localized in topA (the gene for topoisomerase I). The stkD10 mutant has the following characteristics: first, it has an increased abundance of topoisomerase I protein, the topoisomerase I is defective for the DNA relaxation activity, and DNA gyrase activity is reduced; second, the suppressor phenotype of a second mutation localized in rpoH, stkA14 (H. Yigit and W. S. Reznikoff, J. Bacteriol. 179:1704–1713, 1997), can be explained by an increase in topA expression; and third, overexpression of wild-type topA partially suppresses the killing. Finally, topoisomerase I was found to enhance Tn5 transposition up to 30-fold in vivo.     

Lrp4 Domains Differentially Regulate Limb/Brain Development and Synaptic Plasticity

Apolipoprotein E (ApoE) genotype is the strongest predictor of Alzheimer’s Disease (AD) risk. ApoE is a cholesterol transport protein that binds to members of the Low-Density Lipoprotein (LDL) Receptor family, which includes LDL Receptor Related Protein 4 (Lrp4). Lrp4, together with one of its ligands Agrin and its co-receptors Muscle Specific Kinase (MuSK) and Amyloid Precursor Protein (APP), regulates neuromuscular junction (NMJ) formation. All four proteins are also expressed in the adult brain, and APP, MuSK, and Agrin are required for normal synapse function in the CNS. Here, we show that Lrp4 is also required for normal hippocampal plasticity. In contrast to the closely related Lrp8/Apoer2, the intracellular domain of Lrp4 does not appear to be necessary for normal expression and maintenance of long-term potentiation at central synapses or for the formation and maintenance of peripheral NMJs. However, it does play a role in limb development.     

Migration of Myeloid Cells during Inflammation Is Differentially Regulated by the Cell Surface Receptors Slamf1 and Slamf8

Previous studies have demonstrated that the cell surface receptor Slamf1 (CD150) is requisite for optimal NADPH-oxidase (Nox2) dependent reactive oxygen species (ROS) production by phagocytes in response to Gram- bacteria. By contrast, Slamf8 (CD353) is a negative regulator of ROS in response to Gram+ and Gram- bacteria. Employing in vivo migration after skin sensitization, induction of peritonitis, and repopulation of the small intestine demonstrates that in vivo migration of Slamf1^-/- dendritic cells and macrophages is reduced, as compared to wt mice. By contrast, in vivo migration of Slamf8^-/- dendritic cells, macrophages and neutrophils is accelerated. These opposing effects of Slamf1 and Slamf8 are cell-intrinsic as judged by in vitro migration in transwell chambers in response to CCL19, CCL21 or CSF-1. Importantly, inhibiting ROS production of Slamf8^-/- macrophages by diphenyleneiodonium chloride blocks this in vitro migration. We conclude that Slamf1 and Slamf8 govern ROS–dependent innate immune responses of myeloid cells, thus modulating migration of these cells during inflammation in an opposing manner.     

C-terminal domain of the Uup ATP-binding cassette ATPase is an essential folding domain that binds to DNA

The Uup protein belongs to a subfamily of soluble ATP-binding cassette (ABC) ATPases that have been implicated in several processes different from transmembrane transport of molecules, such as transposon precise excision. We have demonstrated previously that Escherichia coli Uup is able to bind DNA. DNA binding capacity is lowered in a truncated Uup protein lacking its C-terminal domain (CTD), suggesting a contribution of CTD to DNA binding. In the present study, we characterize the role of CTD in the function of Uup, on its overall stability and in DNA binding. To this end, we expressed and purified isolated CTD and we investigated the structural and functional role of this domain. The results underline that CTD is essential for the function of Uup, is stable and able to fold up autonomously. We compared the DNA binding activities of three versions of the protein (Uup, UupΔCTD and CTD) by an electrophoretic mobility shift assay. CTD is able to bind DNA although less efficiently than intact Uup and UupΔCTD. These observations suggest that CTD is an essential domain that contributes directly to the DNA binding ability of Uup.     

Cocultivation of Lactococcus lactis and Teredinobacter turnirae for biological chitin extraction from prawn waste

In this study, mainly biological treatment of prawn waste for chitin production was investigated. Lactic acid and protease fermentations were applied to extract chitin from prawn waste in the presence of various glucose concentrations. The results obtained were also compared with those of chemical method which was consisted of first mineral removal and then protein removal sequence. Different strategies were applied using lactic acid producing bacterium, Lactococcus lactis, and a protease producer, marine bacterium Teredinobacter turnirae. Both bacteria were first cultivated individually and then cofermented. In their individual cultivation, L. lactis removed the inorganic materials efficiently, while T. turnirae performed better in deproteinization process. Cofermentation of both bacteria was also conducted using three different protocols. The highest process yield (95.5%) was obtained when T. turnirae was first inoculated. Although the extraction of chitin by biological treatment was incomplete compared to the chemical method, the biological treatment employed here could still be considered as an alternative method in a more environmentally benign approach.