An IS26 variant with enhanced activity

ABSTRACT

The insertion sequence IS26 plays a major role in the mobilization, expression and dissemination of antibiotic resistance genes in Gram negative bacteria. Though IS26 is abundant in sequenced genomes and in plasmids that harbour antibiotic resistance genes, only a few minor variations in the IS26 sequence have been recorded. The most common variant, IS26* (also known as IS15Δ1), encodes a Tnp26 transposase with a single amino acid substitution, G184N in the catalytic domain. Using computational modelling, this substitution was predicted to increase the length of the helix that includes the E173 residue of the catalytic DDE triad, and its effect on activity was tested. An IS26 mutant generated in vitro producing Tnp26-G184N formed cointegrates in a standard untargeted reaction at 4-fold higher frequency than IS26 producing Tnp26. When the target included a single copy of IS26, the G184N substitution increased the cointegration frequency 10-fold and the reaction was targeted and conservative. Hence, the substitution increased Tnp26 activity. The longer helix may stabilise the position of the E173 of the DDE for the catalysis reaction and the specific G184N substitution may also enhance activity by increasing binding to the terminal inverted repeats.

http://bit.ly/2UM7DL7

Resveratrol controls Escherichia coli growth by inhibiting the AcrAB-TolC efflux pump

ABSTRACT

Resveratrol (RSV), a phytoalexin found in grapes and other plants, is known to have antibacterial effects against Escherichia coli. In this study, we aimed to identify the target gene(s) for the antibacterial activity of RSV in E. coli. Using a DNA microarray, we found that exposure to RSV led to changes in the expression levels of iron metabolism genes, and those involved in drug response and respiration. Thus, we measured the antibacterial activity of RSV against fourteen E. coli mutants with deletions in genes involved in these processes and found over fourfold higher growth inhibition in strains defective in AcrAB-TolC pump-related genes. Among the three genes encoding the AcrAB-TolC pump, tolC expression was most decreased by RSV. To determine if tolC was a direct target of RSV, we constructed both a tolC promoter-reporter gene vector and a tolC-complementation vector and transformed them into a tolC deletion mutant. RSV susceptibility and Nile red efflux tests were performed with the transformants. RSV significantly decreased tolC-promoter activity and tolC expression, thereby retarding activity of the AcrAB-TolC drug efflux complex which may promote RSV's antibacterial activity in E. coli.

http://bit.ly/2tjaIHb

Human Spermatogonial Stem Cells Scrutinized under the Single-Cell Magnifying Glass

Spermatogonial stem cells (SSCs) are essential for adult spermatogenesis. Recently, Wang et al. (2018), Guo et al. (2018), and Hermann et al. (2018) used single-cell RNA sequencing to define and molecularly characterize human testicular cell populations, including spermatogonial subsets with characteristics of human SSCs.

http://bit.ly/2SiySQG

We Could Use More Tolerance: Role of Intestinal-Allograft-Derived Human Stem Cells

Mixed chimerism is associated with allograft acceptance and tolerance. In this issue of Cell Stem Cell, Fu et al. (2019) provide evidence that functional, donor-derived hematopoietic stem and progenitor cells in the intestinal allograft can persist long-term, contribute to multi-lineage chimerism in the circulation, and result in T cell tolerance through host lymphoid organ selection.

http://bit.ly/2DcNkzi

Unraveling Difficult Answers: From Genotype to Phenotype in Coronary Artery Disease

Genome-wide association studies (GWASs) have robustly found a correlation between coronary artery disease (CAD) and an intergenic region at locus 9p21.3. However, the mechanistic implication of this association is unknown. Recently in Cell, Lo Sardo et al. used hiPSC genome editing to demonstrate how this locus contributes to CAD predisposition.

http://bit.ly/2SiH9nY

Nerves Do It Again: Donation of Mesenchymal Cells for Tissue Regeneration

Nerves are necessary for proper tissue repair and complex regeneration. Now in Cell Stem Cell, Carr et al. (2019) identify a specific population of mesenchymal cells that reside within nerves and represent a reservoir of precursors that expand in number and differentiate into bone and dermis during tissue regeneration and repair.

http://bit.ly/2Seu2UK

Setting our AdipoSIGHTS on Stem Cells in Pharmacogenomics

In a recent study published in Cell Stem Cell, Hu et al. (2019) used human adipose stem cell-derived adipocytes to demonstrate that genetic variation predicts anti-diabetic response to thiazolidinediones (TZDs) by modulating PPARγ binding.

http://bit.ly/2DmE4J0