Studies of the ribonucleic acid polymerase from Escherichia coli. V. Studies of its complexes with polyribonucleotides.

Abstract The effects of divalent cation and ionic strength on the formation and the sedimentation properties of complexes of DNA-dependent RNA polymerase with polyribonucleotides have been investigated. At low ionic strength and in the presence of divalent cation, the enzyme binds to a polyribonucleotide, forming two complexes with sedimentation values of approximately 15 S and 21 S as detected by sucrose density gradient centrifugation. The 15 S complex is the major one. As the ionic strength is increased, the 21 S and 15 S complexes disappear in that order, and a 13 S complex is detected; then, at a certain ionic strength which varies with the different polyribonucleotides, no complex formation occurs. The polyadenylate-enzyme complex is most sensitive to ionic strength, and the polyuridylate- and transfer RNA-enzyme complexes are least sensitive. At low ionic strength and in the absence of divalent cation, only a 13 S complex is formed. Studies of competition between each of the synthetic polyribonucleotides and transfer RNA for enzyme suggest that the order of reactivity of the polyribonucleotides is as follows: polyadenylate ≅ transfer RNA l polyadenylate-uridylate ≅ polycytidylate l polyuridylate.