Functional analysis of the stem-loop structures at the 5' end of the Aichi virus genome.

Aichi virus is a member of the family Picornaviridae. Computer-assisted secondary structure prediction suggested the formation of three stem-loop structures (SL-A, SL-B, and SL-C from the 5' end) within the 5'-end 120 nucleotides of the genome. We have already shown that the most 5'-end stem-loop, SL-A, is critical for viral RNA replication. Here, using an infectious cDNA clone and a replicon harboring a luciferase gene, we revealed that formation of SL-B and SL-C on the positive strand is essential for viral RNA replication. In addition, the specific nucleotide sequence of the loop segment of SL-B was also shown to be critical for viral RNA replication. Mutations of the upper and lower stems of SL-C that do not disrupt the base-pairings hardly affected RNA replication, but decreased the yields of viable viruses significantly compared with for the wild-type. This suggests that SL-C plays a role at some step besides RNA replication during virus infection.