Inactivation of transfective poliovirion RNA by a product or products of the interaction of trace copper with an impurity or impurities in reagent-grade phenol.

A search for the cause of the inactivation of the transfectivity of the RNA from poliovirions, in the absence of a protective agent such as L-histidine, revealed that the inactivation is associated with trace contamination with copper and with an impurity or impurities in the phenol used to release the RNA from the poliovirions. Cu2+ and the impurity(ies) interact in vitro to produce a proximate inactivator or inactivators of the RNA. Phenol free or nearly free of active impurity can be prepared by steam distillation. Light is not required for formation or for action of the proximate inactivator. Addition of L-histidine to RNA undergoing inactivation promptly stops the inactivation, probably by taking copper away from the proximate inactivator.