Monotonous behavior with 2-propanol converts into reentrant transition with 1-propanol: Higher-order structure of DNA

ABSTRACT In the present study, we measured the changes in the higher-order structure of genomic DNA molecules in the presence of alcohols through single-DNA observation by use of fluorescence microscopy, with particular focus on the different effects of 1-propanol and 2-propanol. The results showed that, with an increasing concentration of 1-propanol, DNA exhibits reentrant conformational transitions from an elongated coil to a folded globule, and then to an unfolded state. On the other hand, with 2-propanol, DNA exhibits monotonous shrinkage into a compact state. Thus, DNA molecules are more effectively condensed/precipitated with 2-propanol than with 1-propanol. The propanol isomers also had different effects on the changes in the secondary structure of DNA, as revealed by circular dichroism (CD) measurements. With 1-propanol, DNA maintains a B-form secondary structure. An A-like conformation appears with the addition of 2-propanol. STATEMENT OF SIGNIFICANCE Currently, 2-propanol has most often been used as the solvent to extract and purify genomic DNA molecules from living cells, according the protocols in molecular biology and biochemistry. Unfortunately, the reason why usage of 2-propanol is recommended instead of ethanol and 1-propanol has never been explained in a clear manner. We believe that the new insight based on chemical physics point of view would play an important role for the development of current chemical procedures/treatments adapted on an empirical basis.