For preparation of core particles,cells were collected 5 days after DNA transfection and suspended in a hypotonic buffer(20 mM Tris-HCl,pH 7.5,50 mM NaCl,5 mM MgCl2,0.1% 2-mercaptoethanol,0.5 mM phenylmethylsulfonyl fluoride).After homgenization,0.2 vol of 40% sucrose was added to the homgenate.The nuclei and mitochondrial fractions were then pelleted by differential centrifugation.The supernatant fraction was loaded onto a 30% sucrose solution in TNE buffer(20 mM Tris-HCl,pH 7.5,0.15 mM NaCl,1 mM EDTA)and centrifuged at 35,000 rpm for 16 hr in a Beckman SW 50.1 rotor.The pellet was subjected to CsCl density gradient centrifugation(1.1-1.6g/cm3)at 35,000 rpm for 18 hr.After fractionation,each fraction was assayed for HBV core antigen/HBV e antigen(HBcAg/HBe.Ag)using the Abbott HBe RIA kit.

具体请参考：http://www.pnas.org/cgi/reprint/84/9/2678.pdf