The double helix: “Photo 51” revisited

Remeasuring the double helix.

DNA is thought to behave as a stiff elastic rod with respect to the ubiquitous mechanical deformations inherent to its biology. To test this model at short DNA lengths, we measured the mean and variance of end-to-end length for a series of DNA double helices in solution, using small-angle x-ray scattering interference between gold nanocrystal labels. In the absence of applied tension, DNA is at...

Transmembrane helix predictions revisited.

Methods that predict membrane helices have become increasingly useful in the context of analyzing entire proteomes, as well as in everyday sequence analysis. Here, we analyzed 27 advanced and simple methods in detail. To resolve contradictions in previous works and to reevaluate transmembrane helix prediction algorithms, we introduced an analysis that distinguished between performance on redund...

Nanotechnology and the double helix.

Seeing beyond the double helix.

Epigenetics, or heritable changes not encoded in the DNA sequence, is a phenomenon important for an overall increase in the complexity of the genome without changes in gene sequence. Our complete genome is contained in each of our cells. Corneal cells are different than nerve cells due to a usage pattern of the genome that is maintained in a cellular memory of active or repressed genes. These “...

Photon efficient double-helix PSF microscopy with application to 3D photo-activation localization imaging

We present a double-helix point spread function (DH-PSF) based three-dimensional (3D) microscope with efficient photon collection using a phase mask fabricated by gray-level lithography. The system using the phase mask more than doubles the efficiency of current liquid crystal spatial light modulator implementations. We demonstrate the phase mask DH-PSF microscope for 3D photo-activation locali...