Genetic characterization of the coxsackievirus B2 3 ' untranslated region

The secondary structure of the 3 ' untranslated region (3 ' UTR) of picorna viruses is thought to be important for the initiation of negative-strand RN A synthesis. In this study, genetic and biological analyses of the 3 ' term inus of coxsackievirus B2 (CVB2), wh ich differs from other enteroviruses d ue to the presence of five additional nucleotides prior to the poly(A) tail , is reported. The importance of this extension was investigated using a 3 ' UTR mutant lacking the five nucleotides prior to the poly(A) tail and con taining two point mutations. The predicted secondary structure within the 3 ' UTR of this mutant was less energetically favourable compared with that of the wild-type (wt) genotype. This mutant clone was transfected into gree n monkey kidney cells in four parallel experiments and propagated for multi ple passages, enabling the virus to establish a stable revertant genotype. Genetic analysis of the virus progeny from these different passages reveale d two major types of revertant. Both types showed wt-like growth properties and more stable and wt-like predicted secondary structures than the parent mutant clone. The first type of revertant neutralized the introduced point mutation with a compensatory second-site mutation, whereas the second type of revertant partly compensated for the deletion of the five proximal nucl eotides by the insertion of nucleotides that matched the wt sequence. There fore, the extended 3 ' end of CVB2 may be considered to be a stabilizing se quence for RNA secondary structure and an important feature for the virus.