STRUCTURE IN THE PRECORE REGION OF HEPATITIS B CORE GENE AFFECTING ITS EXPRESSION IN E.coil

Restriction fragments of HBV-DNA, cleaved by endonuclease HhaI,containing HBcAg gene were trimmed by BAL-31 exonuclease to remove different lengths of the precore sequence.They were inserted into plasmid pUR222 at EcoRI site through synthetic linker ligation. Transformants in E.coli BMH7118 showing different levels of HBcAg gene expression were screened and analyzed for their nucleotide sequences in the junction region both by Maxam and Gilbert's chemical degradation method and by M13 chain termination method. Results of sequence analysis of different transformants revealed a partial palindromic (loop and stem) structure, at -7 to -35 nucleotide with regard to ATG of the HBcAg gene as position +1, which has dramatic effect on the level of expression of the inserted gene using the same promoter,SD sequence and identical N-terminus.The amount of HBcAg synthesized differed from 9% in the high expressing plasmid to less than 0.01% of the total cell proteins in the low expressing transformants.The findings were compared to results obtained by other workers in studies of HBcAg expression in procaryotes and their significance in the expression of eucaryotic genes in procaryotic cells were discussed.

Review on hepatitis B virus precore/core promoter mutations and their correlation with genotypes and liver disease severity

Of 350 million people worldwide are chronically infected with hepatitis B virus(HBV)and are at risk of developing cirrhosis and hepatocellular carcinoma(HCC)later in life.HBV is the most diverse DNA virus,and its genome is composed of four open reading frames:Presurface antigen/surface antigen gene(preS/S),precore/core gene(preC/C),polymerase gene(P),and theχgene(χ).HBV produces quasispecies naturally or in response to antiviral agents because of the absence of proofreading activity amid reverse transcription and a high replication rate.The virus has 10 genotypes(A to J)with different geographical distributions.There are various HBV mutations in the HBV genome,including preC/C mutations,preS/S mutations,P gene mutations,andχgene mutations.The core promoter region plays a vital part in the replication,morphogenesis and pathogenesis of the virus.The precore region also plays a crucial role in viral replication.Both core promoter and precore mutations rescue the virus from host immune surveillance and result in the formation of mutated strains that may have altered pathogenicity.preC/C mutations are associated with liver disease progression.Precore mutations stop hepatitis B e antigen(HBeAg)production and basal core promoter mutations downregulate HBeAg production.Mutations in the basal core promoter are also associated with increased HBV replication and an increased incidence of advanced liver diseases such as cirrhosis and HCC.The emergence of antiviral-resistant mutations is the main reason for treatment failure.This review focuses mainly on preC/C promoter mutations and their correlation with genotypes and liver disease severity.Thorough perception and knowledge of HBV genetic variety and mutants could be vital to discover techniques for the prognosis and control of HBV infection.