Ethanol is a better inducer of DNA guanine tetraplexes than potassium cations.

Guanine tetraplexes are a biologically relevant alternative of the Watson and Crick duplex of DNA. It is thought that potassium or other cations present in the cavity between consecutive guanine tetrads are an integral part of the tetraplexes. Here we show using CD spectroscopy that ethanol induces the guanine tetraplexes like or even better than potassium cations. We present examples of ethanol stabilizing guanine tetraplexes even in cases when potassium cations fail to do so. Hence, besides the A-form or Z-form, ethanol stabilizes another conformation of DNA, i.e., the guanine tetraplexes. We discuss the mechanism of the stabilization. Use of ethanol will permit studies of guanine tetraplexes that cannot be induced by potassium cations or other tetraplex-promoting agents. This work demonstrates that a still broader spectrum of nucleotide sequences can fold into guanine tetraplexes than has previously been thought. Aqueous ethanol may better simulate conditions existing in vivo than the aqueous solutions.