Internal initiation stimulates production of p8 minicore, a member of a newly discovered family of hepatitis C virus core protein isoforms.
The hepatitis C virus (HCV) core gene is more conserved at the nucleic acid level than is necessary to preserve the sequence of the core protein, suggesting that it contains information for additional functions. We used a battery of anticore antibodies to test the hypothesis that the core gene directs the synthesis of core protein isoforms. Infectious viruses, replicons, and RNA transcripts expressed a p8 minicore containing the C-terminal portion of the p21 core protein and lacking the N-terminal portion. An interferon resistance mutation, U271A, which creates an AUG at codon 91, upregulated p8 expression in Con1 replicons, suggesting that p8 is produced by an internal initiation event and that 91-AUG is the preferred, but not the required, initiation codon. Synthesis of p8 was independent of p21, as shown by the abundant production of p8 from transcripts containing an UAG stop codon that blocked p21 production. Three infectious viruses, JFH-1 (2a core), J6/JFH (2a core), and H77/JFH (1a core), and a bicistronic construct, Bi-H77/JFH, all expressed both p8 and larger isoforms. The family of minicores ranges in size from 8 to 14 kDa. All lack the N-terminal portion of the p21 core. In conclusion, the core gene contains an internal signal that stimulates the initiation of protein synthesis at or near codon 91, leading to the production of p8. Infectious viruses of both genotype 1 and 2 HCV express a family of larger isoforms, in addition to p8. Minicores lack significant portions of the RNA binding domain of p21 core. Studies are under way to determine their functions.
Eng
Francis J
FJ
Division of Liver Diseases, Mount Sinai School of Medicine, New York 10029, USA.
Walewski
Jose L
JL
Klepper
Arielle L
AL
Fishman
Sarah L
SL
Desai
Suresh M
SM
McMullan
Laura K
LK
Evans
Matthew J
MJ
Rice
Charles M
CM
Branch
Andrea D
AD
D018387:Codon, Initiator; D016174:Hepacivirus / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D017422:Sequence Analysis, DNA; D014758:Viral Core Proteins / Q000096:biosynthesis* / Q000235:genetics
D018387:Codon, Initiator; D020033:Protein Isoforms; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus