Nuclear import of hepatitis B virus capsids and release of the viral genome

doi:10.1073/pnas.1730940100

Nuclear import of hepatitis B virus capsids and release of the viral genome

^*Institute of Medical Virology, Frankfurter Strasse 107, D-35392 Giessen, Germany; ^‡Swiss Federal Institute of Technology, Institute of Biochemistry, Eidgenössische Technische Hochschule Hoenggerberg, Building HPM, CH-8093 Zurich, Switzerland; and ^†Department of Zoology, University of British Columbia, 6210 University Boulevard, Vancouver, BC, Canada V6T 1Z4

Edited by Francis V. Chisari, The Scripps Research Institute, La Jolla, CA, and approved June 30, 2003 (received for review February 17, 2003)

Abstract

While studying the import of the hepatitis B virus genome into the nucleus of permeabilized tissue culture cells, we found that viral capsids were imported in intact form through the nuclear pore into the nuclear basket. Import depended on phosphorylation of the capsid protein and was mediated by the cellular transport receptors importin α and β. Virus-derived capsids that contained the mature viral genome were able to release the viral DNA and capsid protein into the nucleoplasm. The uncoating reaction was independent of Ran, a GTP-binding enzyme responsible for dissociating other imported cargoes from the inner face of the nuclear pore. Immature capsids that did not contain the mature viral genome reached the basket but did not release capsid proteins nor immature genomes into the nucleoplasm. The different fate of mature and immature capsids after passing the nuclear pore indicates that the outcome of a nuclear import event may be regulated within the nuclear basket.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: michael.kann{at}viro.med.unigiessen.de.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: NPC, nuclear pore complex; Impβ, importin β; Impα, importin α; HBV, hepatitis B virus; PG, pregenomic RNA; NLS, nuclear localization signal; P-C, capsids devoid of viral polymerase; ImmatC, immature capsids; ImmatC-Inh, capsids derived from HepG2.2.15 cells treated with the reverse-transcription inhibitor foscarnet; MatC, mature capsids; EcC, capsid protein in E. coli; EcPC, E. coli-derived recombinant capsids with some of the capsid proteins phosphorylated with trapped PKC; WGA, wheat germ agglutinin.