Low pH RNA-protein interactions in turnip yellow mosiac virus: III. Reassociation experiments with other viral RNAs and chemically modified TYMV-RNA

Abstract

Dissociation-reassociation experiments were performed with turnip yellow mosaic virus in the presence of RNAs extracted from two related viruses: belladona mottle virus and eggplant mosaic virus, containing 32% and 38% cytosine, respectively. Both RNAs interact specifically at low pH with “nascent capsids” of TYMV obtained by dissociation of the virus in 8 M urea, 1 M NaCl, 0.01 M sodium phosphate buffer, pH 7, in the presence of MgCl 2 or spermidine. Up to 80% of the cytosine residues of TYMV-RNA (which contains 38% C) can be modified by bisulfite treatment. But modified TYMV-RNA containing only 32% C (or less) failed to interact with “nascent capsids” at low pH. Bisulfite treatment can also be achieved in the virion and modifies the stability of the particle. It is concluded that it is not the average cytosine content of the RNA that is responsible for the specific low pH RNA-protein interaction, but rather the presence of a special class of cytosine residues located in single-stranded segments of TYMV-RNA. Some peculiarities of the secondary and tertiary structure of TYMV-RNA are also discussed.