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DNA undergoes a helix-to-coil transition (also called denaturation transition) upon heating. This transition can also be facilitated by using solvent mixtures (for example water-alcohol). An increase in the hydrophobic tail of the second solvent molecule first decreases then increases the melting temperature appreciably. Measurement on 4% DNA in a series of water-alcohol mixtures shows that the helix-to-coil melting transition is driven by the solvent ability to cross the hydrophobic sugar-rich region. DNA is behaving like a cylindrical micelle.

The Bacillus subtilis histidine kinase KinA controls activation of the transcription factor governing sporulation, Spo0A. The decision to sporulate involves KinA phosphorylating itself on a conserved histidine residue, after which the phosphate moiety is relayed via two other proteins to Spo0A. The DNA-damage checkpoint inhibitor Sda halts this pathway by binding KinA and blocking the autokinase reaction. We have performed small-angle X-ray scattering and neutron contrast variation studies on the complex formed by KinA and Sda. The data show that two Sda molecules bind to the base of the DHp dimerization domain of the KinA dimer. In this position Sda does not appear to be able to sterically block the catalytic domain from accessing its target histidine, as previously proposed, but rather may effect an allosteric mode of inhibition involving transmission of the inhibitory signal via the four-helix bundle that forms the DHp domain.