Effects of potassium and chloride on ribosome association with the RNA of foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) and other picornaviruses initiate translation of their polyprotein cap-independently at an internal site of the positive-strand viral RNA. This process is mediated by the internal ribosome entry site (IRES), a highly structured cis-acting RNA element that binds translation initiation factors and ribosomal subunits. During their life cycle, picornaviruses induce proliferation of membrane structures involved in viral replication and an increase in membrane permeability probably facilitating virus progeny release. Here, I analyze the efficiency of association of the ribosomal subunits with the FMDV IRES RNA at elevated salt concentrations. Potassium stimulates FMDV translation, whereas sodium chloride concentrations up to 150 mM neither stimulate nor interfere with FMDV translation. Even high potassium concentrations allow binding of the viral RNA to ribosomes. Chloride stimulates binding of ribosomes to the viral RNA at the stage of 48S initiation complex formation and FMDV translation at concentrations up to 150 mM. Only at elevated concentrations, binding of ribosomal subunits and translation are inhibited by chloride. However, FMDV start site selection is not influenced by potassium salts. These results indicate that the association of the viral RNA with ribosomal subunits is well adapted to high salt conditions that are induced during picornavirus infection.