Characterization of nuclear localization of a hepatitis B virus precore protein derivative P22
Both of hepatitis B virus core protein and a precore protein derivative, named P22, have been shown to localize in the nucleus. Although P22 has ten additional amino acid residues at its amino-terminus, both proteins contain the same nuclear localization signal. In order to understand the mechanism that regulates the activity of this signal, we have studied the nuclear localization of P22 and compared it with that of core protein. It was found that both cytosolic and nuclear fractions of P22 were phosphorylated but to a lesser extent when compared with cytosolic core protein. This distinction was likely attributed to different conformations between these two proteins since the density gradient analysis revealed a different particle formation for P22 in the cytosol. When expressed in Vero cells synchronized by serum deprivation, P22 remained in the cytosol during G0 and G1 phases, accumulated gradually in the nucleus during S phase, and largely localized in the nucleus when cells were confluent. On the other hand, the core protein was transported into the nucleus during mid-G1 phase, shuttled back to the cytosol in S phase and again accumulated in the nucleus when cells were confluent. Interestingly, when aphidicolin was used to arrest the cells in late G1 phase, both proteins were found to accumulate in the nuclei. These results indicated that although both P22 and core proteins possessed the same nuclear localization signal, the cellular regulation of their nuclear transport was not identical and might involve different molecular mechanisms.
KeywordsCytosol Nuclear Localization Core Protein Vero Cell Nuclear Localization Signal
Unable to display preview. Download preview PDF.
- 8.Guidotti LG, Martinez V, Loh YT, Rogler CE, Chisari FV (1994) Hepatitis B virus nucleocapsid particles do not cross the hepatocyte nuclear membrane in transgenic mice. J Virol 60: 5469–5475Google Scholar
- 18.Robinson WS (1990) Hepadnaviridae and their replication. In: Fields BN, Knipe DM (eds) Virology. Raven Press, New York, pp 2137–2169Google Scholar
- 19.Roossnick MJ, Jameel S, Loukin SH, Siddiqui A (1986) Expression of hepatitis B virus core regions in mammalian cells. Mol Cell Biol 6: 1391–1400Google Scholar
- 21.Valenzuela P, Quiroga M, Zaldivar J, Gray P, Rutter WJ (1980) The nucleotide sequence of the hepatitis B viral genome and the identification of the major viral genes. In: Fields BN, Jaenisch R, Fox CF (ed) Animal virus genetics. Academic Press, New York, pp 57–70Google Scholar