Roles of the three major phosphorylation sites of hepatitis B virus core protein in viral replication

Hepatitis B virus (HBV) core protein is a phosphoprotein. Its three major p hosphorylation sites have been identified at the serine residues located at amino acids 157, 164, and 172. In order to investigate the role of core pr otein phosphorylation in HBV replication, these three serine residues were mutated to alanine to mimic nonphosphorylated serine or to glutamic acid to mimic phosphoserine. The nonphosphorylated core protein analog did not pac kage the HBV pregenomic RNA, and the phosphorylated analog packaged the pre genomic RNA but failed to support viral DNA replication. These results indi cate that the core protein phosphorylation may be important for pregenomic RNA packaging and that its dephosphorylation may be important for viral DNA replication. The individual roles of these three major phosphorylation sit es in HBV replication were further investigated by being mutated to alanine in different combinations. The results showed that the serine residue at a mino acid 157 was not essential for pregenomic RNA packaging, whereas the s erine residues at amino acids 164 and 172 were more important Furthermore, the serine residue at amino acid 157 was not essential for viral DNA replic ation or viral maturation. (C) 1999 Academic Press.