The Adeno-Associated Virus Replicase Rep78 Contains a Strictly C-Terminal Sequence Motif Conserved Across Dependoparvoviruses

Adeno-Associated Viruses (AAVs, genus Dependoparvovirus) are the leading gene therapy vector. Until recently, efforts to enhance their capacity for gene delivery had focused on their capsid. However, efforts are increasingly shifting towards improving the viral replicase, Rep78. We discovered that Rep78 and its shorter isoform Rep52 contain a strictly C-terminal sequence motif, DDx3EQ, conserved in most dependoparvoviruses. The motif is highly negatively charged and devoid of prolines. Its wide conservation suggests that it is required for the life cycle of dependoparvoviruses. Despite its short length, the motif’s strictly C-terminal position has the potential to endow it with a high recognition specificity. A candidate target of the DDx3EQ motif might be the DNA-binding interface of the origin-binding domain of Rep78, which is highly positively charged. Published studies suggest that the motif is not required for recombinant AAV production, but that substitutions within it might improve production.