Fig. 2From: Hepatitis B virus virion secretion is a CRM1-spike-mediated late eventThe tip of the spike at HBc 76–89 is required for secretion of both genome-containing virions and naked capsids. A Site-directed mutations were introduced into amino acid L65, L76, V85, V89 and L95 (red colored) of NES-I and NES-II. These mutants accumulated HBc in the nucleus as described [29]. B Intracellular core-associated RNA and DNA genomes were analyzed by Northern blot and Southern blot. None of these HBc mutants are defective in packaging the 3.5 kb full-length pgRNA. Except L95A, mutants L65A, L76A, V85A, V89A exhibited some minor defect in RC DNA synthesis. All results shown in (D) represent one of three independent repeat experiments. The vertical dotted line indicates splicing of data from the same gel. C Extracellular HBV particles were analyzed by the method illustrated in Additional file 1: Fig S1A. Single mutation L76A, V85A, V89A inhibited secretions of both genome-containing virions and naked capsids. However, mutation L95A inhibited only genome-containing virion secretion, but no effect on naked capsid secretion. All results shown in (B) represent one of three independent repeat experiments. The vertical dotted line indicates splicing of data from the same gel. D The tip of spike is a hub of multiple trafficking signals of HBc particles. Comparisons of important amino acid residues of HBc involved in HBc nuclear export, virion and naked capsid secretions. E A three dimentional view (PDB code 1QGT) of HBc dimer which can assemble into an icosahedral particle. Key HBc amino acid residues involved in the secretion of particles, as highlighted in (C), are clustering at the tip of the spike of HBc capsids. Red: secretion of genome-containing virions. Blue: secretion of naked capsids. Merge: purple. For comparison, we included a previous map of amino acids at the bottom of the spike, which are also involved in the secretion of HBV genome-containing virions (cyan) [37]. This figure was produced using PyMOL (Schrödinger, LLC; http://www.pymol.org)Back to article page