A single adaptive point mutation in Japanese encephalitis virus capsid is sufficient to render the virus as a stable vector for gene delivery.

Japanese encephalitis virus (JEV) is a neurotropic flavivirus that has broad range of hosts. Stable JEV vector has not been reported yet. Here, we constructed a JEV-EGFP by inserting a fragment of C38 (the N-terminal 38 amino acids of capsid)-EGFP-FMDV2A into the junction between 5'UTR and the N-terminus of capsid gene. An adaptive nucleotide mutation T45G (location at the N-terminus of capsid gene), resulting in an amino acid change from asparagine to lysine (N15K), was identified by genome sequencing. It stabilized the vector and enlarged the virion. The stabilizing effect might be general because it is also stable when EGFP was replaced with another marker, SNAP. A model was proposed for this stabilization effect based on previously published and our data. This finding may be used to construct various JEV-based stable delivery systems for virological studies and neural circuit tracing.