Stem cells

Human induced pluripotent stem cells with a clean genome

Reprogramming of differentiated cells to induced pluripotent stem cells was initially achieved using integrating viruses to deliver the reprogramming factors. This can cause abnormalities in the cells and is undesirable particularly for therapeutic applications. Yu et al. now reprogram human fibroblasts using the oriP/EBNA1 vector to deliver the reprogramming factors. This vector forms a stable episome and is lost from cells in the absence of drug selection.

Yu, J. et al. Science advance online publication (26 March 2009).


Finding inhibitors with ABPP

Activity-based protein profiling (ABPP), which uses reactive chemical probes to target enzyme active sites, can be used to elucidate the function of uncharacterized enzymes. Bachovchin et al. now adapt ABPP to a competitive inhibitor screen using fluorescence polarization, which monitors the apparent size of a fluorophore-tagged activity-based probe (whether it binds to the enzyme or not). This allows them to screen very large compound libraries, unlike the previous gel-based readout.

Bachovchin, D.A. et al. Nat. Biotechnol. 27, 387–394 (2009).


Inherited transcriptional errors

Mutations that are passed on to daughter cells are usually caused by changes in the DNA sequence. Errors in transcription, leading to mutation in the RNA, are as short lived as the RNA itself and thought to have no impact on the heritable phenotype. Gordon et al. now show with a bistable lac operon that the molecular noise caused by transcriptional errors can trigger a positive feedback loop that results in a heritable phenotypic difference in genetically identical cells in the same environment.

Gordon, A.J.E. et al. PLoS Biol. 7, e1000044 (2009).

Protein biochemistry

Reverse micelles for nuclear magnetic resonance

Membrane proteins are notoriously difficult to study with nuclear magnetic resonance spectroscopy owing to their need to be solubilized in large detergent micelles, which prevents rapid molecular tumbling needed for optimal data collection via triple-resonance experiments. Kielec et al. now use reverse micelles, a micelle that has flipped its orientation in a low-viscosity organic solvent, and thus facilitates fast molecular tumbling, to investigate the structure of a potassium channel.

Kielec, J.M. et al. Structure 17, 345–351 (2009).


Ultrastable AFM

Instrumental drift in atomic force microscopy (AFM) is a critical problem that limits imaging resolution. Sharper tips and high-sensitivity detection methods can improve resolution, but rapid scanning is still required to minimize instrumental drift. King et al. now describe a different solution to stabilize the AFM stage: they scatter laser light off the apex of the AFM tip to create a local frame of reference. This permits them to control the position of the AFM tip with high precision, allowing them to scan slowly, improving imaging resolution.

King, G.M. et al. Nano Lett. 9, 1451–1456 (2009).