The activity on double-stranded RNA of aggregates of ribonuclease A higher than dimers increases as a function of the size of the aggregates

Stable bovine RNase A aggregates larger than dimers (identified as trimers, tetramers, pentamers and hexamers) were obtained by lyophilization of RNase A from 40-50% acetic acid solutions. The RNase activity of these aggregates was compared with that of monomeric RNase A on single- and double-stranded polyribonucleotides. Their activity toward poly(U) and yeast RNA slightly decreases as a function of the size of the aggregates. In contrast, their action on poly(A).poly(U) as substrate progressively increases from a relative activity of 1 for the RNase monomer to 10 for the hexamer. These results are discussed in the light of an already advanced hypothesis about a possible mechanism of RNase attack on double-stranded RNA.