Hepatitis B virus maturation is affected by the incorporation of core proteins having a C-terminal substitution of arginine or lysine stretches.
Assembly of replication-competent hepadnavirus nucleocapsids requires interaction of core protein, polymerase and encapsidation signal (epsilon) with viral pregenomic RNA. The N-terminal portion (aa 1-149) of the core protein is able to self-assemble into nucleocapsids, whereas the C-terminal portion (aa 150-183) is known to interact with pregenomic RNA. In this study, two hepatitis B virus (HBV) core mutants (C144Arg and C144Lys) in which the C-terminal SPRRR (Ser-Pro-Arg-Arg-Arg) motif was replaced by a stretch of arginine or lysine residues were generated to test their role in pregenome encapsidation and virus maturation. Mutant or wild-type core-expression plasmids were co-transfected with a core-negative plasmid into human hepatoma HuH-7 cells to compare trans-complementation efficiency for virus replication. Both low- and high-density capsids were present in -the cytoplasm and culture medium of HuH-7 cells in all transfections. Nucleocapsids formed by C144Arg and C144Lys, however, lost the endogenous polymerase activity to repair HBV DNA. Furthermore, in co-transfection of pHBVC144Arg or pHBVC144Lys with a plasmid which produces replication-competent nucleocapsids, the HBV DNA repairing signal was reduced 40- to 80-fold. This is probably due to formation of mosaic particles of wild-type and mutant cores. Results indicated that the SPRRR motif at the core protein C terminus is important for HBV DNA replication and maturation. Additionally, triple-plasmid transfection experiments showed that nucleocapsids containing various amounts of C144Arg and wild-type core proteins exhibited a bias in selecting a shorter pregenome for encapsidation and DNA replication. It is therefore suggested that unknown factors are also involved in HBV pregenome packaging.
Hui
Eric Ka-Wai
EK
Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1.
Chen
Kun-Lin
KL
Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1.
Lo
Szecheng J
SJ
Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1.
D019943:Amino Acid Substitution; D001120:Arginine / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D006512:Hepatitis B Core Antigens / Q000235:genetics / Q000502:physiology*; D006515:Hepatitis B virus / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008239:Lysine / Q000235:genetics / Q000502:physiology*; D019251:Nucleocapsid / Q000502:physiology; D011494:Protein Kinases / Q000378:metabolism; D012322:RNA Precursors; D014407:Tumor Cells, Cultured; D014771:Virion / Q000502:physiology; D019065:Virus Assembly
D006512:Hepatitis B Core Antigens; D012322:RNA Precursors; D001120:Arginine; D011494:Protein Kinases; D008239:Lysine