Differential, structure-dependent susceptibility of poly(A) and RNA to monomeric and dimeric pancreatic ribonuclease A.

Cross-linked dimers of bovine RNAase A are definitely more efficient than monomers at degrading polyadenylic acid under conditions of ionic strength and pH, where the polymer assumes either a double-helical or an ordered single-stranded, base-stacked structure. The opposite occurs, i.e., monomers of RNAase A are definitely more active than dimers,when poly(A) is digested by the two enzyme species under conditions where the conformation of the polymer is essentially that of a random coil. The same pattern of events occurs when total RNA from Escherichia coli or single-stranded RNA of f2 sus11 bacteriophage are used as substrates under opposite ionic-strength conditions. In the presence of high salt concentrations, favouring the formation and the stability of a secondary structure in self-complementary sequences of RNA, the ribonucleic acids are degraded at a higher rate by dimers than by monomers of bovine RNAase A. The opposite occurs in the presence of very low salt concentrations, i.e. when the RNAs are in solution presumably as random coils. These observations are discussed in the light of a hypothesis already advanced to understand the mechanism of enzymic degradation of secondary structures of polyribonucleotides.