Fig. 6

Only the small envelope protein can rescue the virion secretion defect of the proline substitution mutant M198P. A A cartoon illustrates that the envelope protein ORF can encode a total of 6 different protein products, including large, middle and small envelope proteins. A proline substitution mutation (red asterisk*) is supposed to be present in all 6 envelope proteins. B Western blot analysis detected respective protein products from large, middle and small envelope protein expression vectors. This expression vector is a core-null replicon, which contains no core protein, and is expressing a wild type polymerase and various mutant envelope proteins. Left panel outlines the respective mutations at the initiation codons of large, middle, and small envelope proteins. C Cotransfection with the core-null replicon containing large or middle envelope protein did not restore virion secretion. Only the small envelope protein can successfully rescue the virion secretion defect of the small loop mutant M198P. Red asterisk * highlights the HBc core protein signal and HBV DNA signal by complementation with the small S envelope protein. Virion-associated DNAs were quantified by densitometry and Image J software. D Virion-associated HBV DNA was analyzed by qPCR as described in Fig. 4B. HBV DNA signals of the complementation experiments were compared individually to the mutant M198P. GE: genomic equivalent. Bar graph statistics by one-way ANOVA tests. ***P < 0.001