Isostable DNA

The greater stability of G·C DNA base pairs compared to that of A·T base pairs can introduce bias into DNA applications such as the use of microarrays. Ahlborn et al. now make isostable DNA by chemically modifying nucleic acids, introducing caps, locks and intercalators on target all-(A+T) strands to stabilize interactions and N 4-ethylcytosine residues on target all-(G+C) strands to tune down the stability. The use of these 'decorated' nucleic acids is compatible with existing microarray platforms.

Ahlborn, C. et al. J. Am. Chem. Soc. 129, 15218–15232 (2007).

Cell biology

Separating cells by cell-cycle phase

Methods for separating cells according to cell-cycle phase are important for many biotechnology applications, but gentle ways to do so without introducing cell stress are lacking. Kim et al. describe a dielectrophoresis-based microfluidic device that gently separates mammalian cells by taking advantage of the relationship between cell-cycle phase and the cell volume—G2/M phase cells are much larger than G1/S phase cells.

Kim, U. et al. Proc. Natl. Acad. Sci. USA 104, 20708–20712 (2007).


Assembling bacterial genomes

High-throughput sequencing technologies produce an unprecedented amount of data—in the form of short reads. To assemble a whole genome from sequence fragments of no more than 300 bp in length is a computational challenge. Chaisson and Pevzner now present a new Eulerian assembler that generates long contigs from 454 sequence reads that can then be assembled into the full genome with the help of low-coverage Sanger reads.

Chaisson, M.J. & Pevzner, P.A. Genome Res., published online December 14, 2007.


Dynamic protein interactions in live cells

Understanding signaling pathways requires analysis of their dynamic and interacting protein components. Fluorescence fluctuation spectroscopy methods can be used for such studies, but have not been extensively applied to live cells. In recent work, Slaughter et al. used such fluctuation techniques, along with imaging, to study the diffusion dynamics, stoichiometries and interactions between components of the MAP kinase cascade in living yeast.

Slaughter, B.D. et al. Proc. Nat. Acad. Sci. 104, 20320–20325 (2007).


Super-resolution in 3D

The diffraction limit of light microscopy has recently been broken with several new techniques. However, super-resolution in all three dimensions has remained challenging. Now, using optical astigmatism in combination with their two-dimensional STORM method, Huang et al. achieved three-dimensional super-resolution imaging, with 20–30 nm lateral and 50–60 nm axial resolution.

Huang, B. et al. Science, published online 3 January 2008.