Inhibition of purified wheat germ DNA dependent RNA polymerase by pyran copolymer

The inhibition of DNA and RNA polymerases in vitro by pyran copolymer has been shown to be related to its affinity for divalent cations. The present investigation was designed to explore further the nature of this inhibition using completely purified eukaryotic RNA polymerase II from wheat germ. Inhibition was determined as a function of divalent ion concentration and, as previously seen with less pure enzyme preparation, was greatest at low (Mn2+) and least at higher concentrations. No inhibition was observed at concentrations greater than 4.8 mM MgCl2 in the presence of 10 micrograms pyran/mL. The inhibition by pyran copolymer was exerted immediately unlike other polyanions, such as heparin and polynucleotides. This indicates that it stops RNA chain growth immediately as do known chelators of divalent cations. The size of pyran copolymer was shown to affect the extent of inhibition when different sized polymers were fractionated from a heterogenous single lot. However, when sized fractions were obtained from different lots we could not show a size-dependent inhibition. Although the mechanisms by which pyran copolymer exerts its biological effect is unknown, it may well be related to its association with cations. The inhibition of enzymes requiring these cations appears to be a sensitive method of observing such an association.