THE B-FORM TO Z-FORM TRANSITION OF POLY(DG-M(5)DC) IS SENSITIVE TO NEUTRAL SOLUTES THROUGH AN OSMOTIC-STRESS

Several neutral solutes, ranging in size from methanol to a tetrasacch aride, stachyose, are shown to stabilize the left-handed Z form of the methylated polynucleotide poly(dG-m(5)dC). The action of these solute s is consistent with an osmotic stress, that is, with their effect on water chemical potentials coupled to a difference in the number of-ass ociated water molecules between the B and Z conformations. The apparen t difference in hydration between the two forms is, however, dependent on the particular solute used to probe the reaction. The effect of so lutes is not consistent either with a direct binding of solute or with an indirect effect on electrostatics or ion binding through changes i n the solution dielectric constant. The interplay of NaCl and neutral solute in modulating the B-Z transition suggests that salt also could be stabilizing the Z form through an osmotic stress.