Effect of guanidinium ion on DNA denaturation and renaturation

Guanidinium chloride (GuCl) in concentrated solutions has been used in denaturing proteins (Tanford, Kawachara and Lapanje 1967) and for this reason, it has also been suggested for use in the isolation of nucleic acids from nucleoproteins (Cox 1968). While there is no apparent effect of this procedure on the products so isolated, little has been reported as to its action on DNA alone. Rice and Doty (1957) observed earlier that the decrease in intrinsic viscosity of calf thymus DNA occurred at a lower temperature in 3.2 M GuCl than in 0.8 M NaCl, but 8 M urea was more effective than 3.2 M GuCl. The present studies employ the measurement of the absorbance-temperature profile (Rice and Doty 1957, Cavalieri and Rosenberg 1957, Marmur and Doty 1962) and show that the degree of stabilization of DNA helicity by GuCl at low ionic strength is proportional to the molarity of the salt, whereas at high concentrations, the reverse is the case. Thus, the results suggest a unique, dual effect of GuCl uncommon to most denaturants.