PROPERTIES OF HEPATITIS-B VIRUS PRE-S1 DELETION MUTANTS

Deletion mutants of hepatitis B virus (HBV) pre-S proteins were detect ed in serum in 2 of 10 (20%) individuals with chronic hepatitis B infe ction following the initiation of interferon treatment. The size of th ese deletions was up to one-half of the entire pre-S1 region. In vivo, all HBV deletion mutants were found to coexist with a full-length ''w ild-type'' viral genome. The functional properties of a HBV-deleted mu tant were studied in detail and revealed a stop codon in the pre-S2 op en reading frame in all 20 of the clones sequenced. Several of the del eted mutants produced low-level HBsAg in culture supernatants compared to wild-type virus due to a putative loss of transcription factor bin ding sites. Transfection experiments in human hepatoma cells (HuH-7) d emonstrated that the polymerase gene function was not affected by the large pre-S1 deletions and mutant viral genomes were capable of replic ation. However, secretion of incapsidated mutant viral genomes was blo cked in HuH-7 cells. Cotransfection studies with a plasmid expressing only the HBV pre-S1, pre-S2, and S proteins resulted in complete resto ration of viral particle secretion. Our findings suggest that an in vi vo trans-complementation phenomenon would have had to occur to permit secretion from the liver into serum of the nucleocapsids containing th ese deleted viral genomes. (C) 1994 Academic Press, Inc.