Coxsackievirus B3 (CV-B3) is a cardiovirulent enterovirus that utilizes a 5' untranslated region (5'UTR) to complete critical viral processes. Here, we directly compared the structure of a 5'UTR from a virulent strain with that of a naturally occurring avirulent strain. Using chemical probing analysis, we identified a structural difference between the two 5'UTRs in the highly substituted stem-l...