A coding RNA sequence acts as a replication signal in cardioviruses

Theiler's virus and Mengo virus are representatives of the Cardiovirus genu s within the picornavirus family, Their genome is an 8-kilobase long positi ve strand RNA molecule. This RNA molecule plays three roles in infected cel ls: It serves as a messenger RNA, acts as a template for genome replication , and is encapsidated to form progeny virions. We observed that a cis-actin g signal required for replication of Theiler's virus was contained within a 130-nt stretch of the region encoding the capsid protein VP2. This RNA seq uence does not influence internal ribosome entry site-mediated translation initiation and thus likely acts directly as a signal for the replication co mplex. We found a similar signal in the VP2-coding sequence of Mengo virus, and both signals could be functionally exchanged. Within the replication e lement, a 9-nt sequence that is highly conserved among cardioviruses was sh own to be essential for replication. This conserved sequence was contained in mostly unpaired regions of the RNA secondary structure predicted for the replication elements of the various cardioviruses. Interestingly, a simila r replication element has been reported to occur in the distantly related h uman rhinovirus type 14, suggesting that such elements could be conserved t hroughout the picornavirus family. However, the different location of the r eplication elements in rhinovirus and cardioviruses, and the fact that they were not functionally exchangeable, is raising intriguing questions about the evolution of such signals in picornaviruses.