Subtype-independent immature secretion and subtype-dependent replication deficiency of a highly frequent, naturally occurring mutation of human hepatitis B virus core antigen

The most Frequent mutation of the human hepatitis B virus (HBV) core antige n occurs at amino acid 97. Recently, a phenylalanine (F)-to-leucine (L) mut ation at this position (mutant F97L) in HBV surface antigen subtype ayw has been shown to result in an immature secretion phenotype, which is characte rized by the nonselective export of an excessive amount of virions containi ng minus-strand, single-stranded HBV DNA. While subtype ayw mutant F97L has been found in Europe, the major reservoir of HBV resides in Asia and Afric a. We report here that the immature secretion phenotype indeed can be found in an HBV strain (subtype adr) prevalent in Asia, changing from an isoleuc ine (I) to a leucine (mutant 197L). Despite its immature secretion phenotyp e, the adr variant I97L replicates as well as its parental adr wild-type I9 7I, supporting the conclusion that the extracellular phenotype of immature secretion is not a consequence of the intracellular HBV DNA replication def ect. Further studies demonstrated that it is the acquisition of a leucine, rather than the loss of a wild-type amino acid at codon 97, that is importa nt for immature secretion. We conclude that immature secretion is a subtype -independent phenotype and deficiency in intracellular DNA synthesis is a s ubtype-dependent phenotype, The former is caused by the trans-acting effect of a mutant core protein, while the latter by a cia-acting effect of a mut ated nucleotide on the ayw genome. These immature secretion variants provid e an important tool for studying the regulation of HBV virion assembly and secretion.