Hepatitis B virus core antigen has two nuclear localization sequences in the arginine-rich carboxyl terminus

Abstract

Expression of the hepatitis B virus core antigen (HBcAg) in mouse NIH 3T3 fibroblasts has been shown previously (A. McLachlan et al., J. Virol. 61:683-692, 1987) to result in the nuclear localization of this polypeptide. Since the carboxyl terminus of HBcAg contains four clusters of arginine residues which resemble nuclear localization sequences identified in other nuclear proteins, a series of carboxyl-terminus-truncated HBcAg polypeptides were expressed in mouse fibroblasts to examine the role of these sequences in the cellular localization of HBcAg. By immunofluorescence and cell fractionation analysis, it was demonstrated that regions of the HBcAg polypeptide including the most carboxyl-terminal (cluster 1) and amino-terminal (cluster 4) clusters of arginine residues represent distinct and independent nuclear localization sequences for this polypeptide. Substitution of a threonine residue for the second arginine residue in cluster 4 inactivates the nuclear localization signal in this region of the HBcAg polypeptide, demonstrating the importance of this residue to this signal sequence. However, HBcAg fails to accumulate in the nucleus only when both nuclear localization signal sequences are simultaneously deleted or disrupted by mutation. The possible significance of the nuclear localization sequences identified in the HBcAg polypeptide is discussed in the context of the role of the nucleocapsid in the hepatitis B virus life cycle.

Nucleolar Localization of Human Hepatitis B Virus Capsid Protein

“…The cells were fixed by the acetone-methanol fixation method. known role in nuclear targeting (20,29,70,71). It is common that nuclear and nucleolar localization sequences overlap, and the latter has been reported to be longer and more stringent than the former (37).…”

HLA-A31- and HLA-Aw68-restricted cytotoxic T cell responses to a single hepatitis B virus nucleocapsid epitope during acute viral hepatitis.

“…6), which are identical except for the presence of a 29-residue amino-terminal signal sequence in the precore protein that directs it to the endoplasmic reticulum where 19 amino-terminal residues and 34 carboxyterminal residues (residues 149-183) are removed and the product is secreted via the Golgi apparatus into the serum as HBeAg. In contrast, the core protein lacks the signal sequence and is targeted principally to the nucleus by a series of arginine-rich localization signals at its carboxy terminus (20); one of which (residues 145-156) also plays a critical role in viral RNA encapsidation (21). It is interesting that residues 141-151 are involved in all of these important events in the virus life cycle.…”

G1 phase dependent nuclear localization of relaxed-circular hepatitis B virus DNA and aphidicolin-induced accumulation of covalently closed circular DNA

“…Obviously, this protein plays an important role in inhibiting the amplification of cccDNA. Core protein itself has also been suggested to play a role in regulating cccDNA levels [Eckhardt et al, 1991;Yeh et al, 1993;Kann and Gerlich, 1994;Liao and Ou, 1995]. To carry the viral DNA through the nuclear pore, the nucleocapsids have to be at least partially dissembled into sub-particles, since an intact core particle cannot enter the nuclei in the transgenic mice experiment [Bock et al, 1994;Guidotti et al, 1994].…”