Amino acid sequence of the f 2 coat protein

Abstract

The effect of the anionic detergent sodium dodecyl sulfate (SDS) on a number of simple isometric RNA viruses and empty capsids was tested. Some viruses showed extreme sensitivity, e.g., cucumber mosaic (CMV), brome mosaic (BMV) and alfalfa mosaic (AMV) virus, some extreme resistance, e.g., turnip yellow mosaic (TYMV) and tomato bushy stunt (TBSV) virus, and some intermediate resistance, e.g., southern bean mosaic virus (SBMV) and bacteriophage f2, to dissociation into components by this detergent. In the viruses most sensitive to SDS, virion dissociation is apparently caused by disruption of the electrostatic protein-RNA interactions which are responsible for stabilizing the virions. It is proposed that dodecyl sulfate (DS−) ions bind by means of the hydrocarbon chain to specific binding sites on the virion so that the sulfate groups are near lysine- or arginine-phosphate interaction points; these interactions are neutralized and the phosphates are repulsed, resulting in virion dissociation. Based on this hypothesis several predictions were made, tested experimentally and found valid: (1) Virions become more resistant to SDS as the contribution of the protein-protein interactions to virus stability increases. This was confirmed by testing the sensitivities of a number of viruses, including those mentioned above, to SDS. (2) Capsids devoid of nucleic acid are less sensitive to SDS than the respective intact virions. The behavior of TYMV, BMV and bacteriophage f2 virions and capsids with SDS confirmed this prediction. (3) Positive and neutral detergents do not cause dissociation of the SDS-sensitive viruses. (4) Reassembly of viruses stabilized by protein-RNA interactions is inhibited by SDS but not by positive detergents. Predictions (3) and (4) were confirmed by appropriate experiments with CMV or BMV and SDS, dodecyltrimethylammonium chloride (DTAC) and Triton-X-100. Measurements of amounts of detergent bound at low SDS concentrations showed that CMV and BMV have much greater affinitives than TYMV for DS− ions. It is suggested that SDS is useful as a probe for protein-RNA interactions and that relative sensitivity to SDS could be used in categorizing viruses according to stabilizing interactions.