Identification of a DNA encapsidation sequence for human polyomavirus pseudovirion formation

Human polyomavirus is a naked capsid virus containing a closed circular double-stranded DNA genome. The mechanism of DNA encapsidation for the viral progeny formation is not fully understood. In this study, DNA encapsidation domain of the major capsid protein, VP1, of the human polyomavirus JCV was investigated. When the first 12 amino acids were deleted, the E. coli expressed VP1 (Delta N12VP1) failed to encapsidate the host DNA although the integrity of the capsid-like structure was maintained. In addition, capsid-like particles of Delta N12VP1 did not package exogenous DNA in vitro, which is in contrast to that of the full-length VP1 protein. These findings suggest that the N-terminal of the first 12 amino acids of VP1 were responsible for DNA encapsidation. The importance of amino acids in the DNA encapsidation domain was determined further using site-directed mutagenesis. All of the positively charged amino acids at the N-terminal region of VP1 were essential for DNA encapsidation. The results indicate that the N-terminal region of the human polyomavirus major capsid protein VP1 may be involved in viral genome encapsidation during progeny maturation.