Determination of a putative recombinogenic human hepatitis B virus sequence and its binding cellular protein

Previously, we reported that C4BglII196, a 196-base pair subgenomic fragment of hepatitis B virus (HBV) covering its precore region, enhances in vitro recombination in the presence of extracts from actively dividing cells (Hino, O., et al. Proc. Natl. Acad. Sci. USA, 88:9248-9252, 1991). The results indicated that HBV may play some role in causing genomic instability during chronic hepatitis. In the present study, we showed that 15AB, a 60-base pair subgenomic fragment of HBV DNA (nucleotides 1855-1914) within C4BglII196 is indispensable for enhancement of in vitro recombination, using the mouse leukemia cell 70Z/3, as the cellular extract source. 15AB, thought to be the encapsidation signal of HBV pregenomic RNA and U5-like retrovirus long terminal repeat, was found to bind specifically to an approximately 100 kDa protein of 70Z/3 by southwestern blotting. Production of a mutation in the 15AB region decreased both its binding activity to 100 kDa protein and the in vitro recombination activity. Our present results thus suggest that 15AB might be a recombinogenic sequence and the 100-kDa protein may be a putative recombinogenic protein in eukaryotes, triggering genomic instability and facilitating carcinogenesis.