[Interaction of oligoadenylic acids with repolymerized protein of tobacco mosaic virus].

Interaction of oligoadenylic acids (pA) n, n = 3 to 6, with the protein of tobacco mosaic virus has been studied by methods of equilibrium dialysis, gel filtration, and precipitation of the complex by centrifugation. It has been found that oligo(A) forms specific complexes with virus-like helical protein aggregates (HPA), but does not interact neither with double disks nor other small protein aggregates. Interaction becomes stronger when pH and/or ionic strength are decreased. The binding of (pA)3 to HPA decreases with temperature, whereas the binding of longer oligonucleotides increases. The binding constants for the interaction of (pA)3 with HPA in 0,1 M acetate pH 5.50 have been found to be equal 510 +/- 70 at 30 degrees C and 1960 +/- 250 at 0 degrees C. In the case of (pA)3 the binding equilibrium is reached within minutes at T greater than or equal to 20 degrees C; 15 h is needed for the same at 0 degrees C. The binding of oligonucleotides containing four or more residues proceeds at a much lower rate. For instance, in the case of (pA)5 the equilibrium is not reached even within 200 hours at 0 degrees C or 48 hours at 30 degrees C. Two possible mechanisms of interaction are discussed: (1) direct interaction of oligonucleotides with the inner part of protein aggregate through the central hole of the particle due to the fluctuational opening of the V-helices (2) binding of oligonucleotides on the end surfaces of HPA followed by their redistribution along the particle due to the end-to-end association and disruption of particles. A hypothesis concerning the phasing of RNA in the initiation complex is advanced making use of the data of J.J. Steckert and T. M. Schuster.