Mechanism of suppression of hepatitis B virus precore RNA transcription bya frequent double mutation

A double mutation which converts nucleotide 1765 from A to T and nucleotide 1767 from G to A is frequently found in the hepatitis B virus (HBV) genome isolated from HBV patients with chronic hepatitis symptoms. This double mu tation is located in the core promoter that controls the transcription of t he precore RNA and the core RNA. In addition, this double mutation also res ides in the X protein coding sequence, converting codon 130 from Lys to Met and codon 131 from Val to Ile. Previous studies indicate that this double mutation removes a nuclear receptor binding site in the core promoter, supp resses specifically precore RNA transcription, and enhances viral replicati on. In this study, we further investigated how this double mutation suppres ses precore RNA transcription. We found that this double mutation not only removed the nuclear receptor binding site but also created an HNF1 transcri ption factor binding site. Further transfection studies using Huh7 hepatoma cells indicate that the removal of the nuclear receptor binding site has n o effect on the transcription of HBV RNAs, the two-codon change in the X pr otein sequence suppresses the transcription of both precore and core RNAs, and the creation of the HNF1 binding site restores the core RNA level. Henc e, the specific suppression of precore RNA transcription by this frequent d ouble-nucleotide mutation is the combined result of multiple factors.