The presence of the ssDNA band in pIHBoV1-transfected HEK293 cells suggested that progeny virions were produced. To prove this, we carried out large-scale pIHBoV1 transfection and CsCl equilibrium centrifugation to purify the virus that was produced. We fractionated the CsCl gradient, and found the highest HBoV1 gc (1-5610 8 gc/ml) at a density of 1.40 mg/ml, which is typical of the parvovirus virion. Electron microscopy analysis revealed that purified virus displayed a typical icosahedral structure, with a diameter of ,26 nm ( Figure 2E ).