Summary auto-generated
This study compared the translation efficiency of internal ribosome entry sites (IRES) in the 5' untranslated region (5'UTR) of hepatitis C virus (HCV) across all six major genotypes. Researchers cloned and sequenced 5'UTR regions from HCV isolates representing genotypes 1a, 1b, 2b, 3a, 4a, 5a, and 6a, then inserted them into a bicistronic dual luciferase reporter construct. The construct was transfected into four different cell lines (BHK-21, HeLa-T4+, HuH7, and HepG2) using a vaccinia virus T7 system. Translation efficiency was measured by comparing the activity ratio of two luciferase enzymes—one driven by the HCV IRES (cap-independent) and one by cap-dependent scanning. The genotype 2b IRES was the most efficient at directing translation across all cell lines tested, while genotype 6a was generally the least efficient. In HepG2 cells specifically, the 2b IRES was approximately three-fold more active than the 6a IRES. These findings suggest that despite the high conservation of HCV 5'UTR sequences and secondary structures, subtle differences between genotypes result in functional variations in translation initiation efficiency.
Key findings
- Genotype 2b hepatitis C virus has the most efficient IRES-mediated translation across all tested cell lines, while genotype 6a is the least efficient.
- Translation efficiency varies significantly by cell type, with HepG2 and BHK-21 cells showing approximately 2-fold higher HCV IRES activity than HeLa-T4+ or HuH7 cells.
- Despite only 17 nucleotide differences between the most and least active IRES elements, these sequence variations produce substantial functional differences in translation initiation.
- Different HCV genotypes show relatively similar translation efficiencies except for genotypes 2b and 6a, suggesting subtle secondary structure effects modulate IRES activity.
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Abstract
The 5' untranslated region (5'UTR) of hepatitis C virus (HCV) contains an internal ribosome entry site (IRES) which directs translation of the viral open reading frame (ORF). The 5'UTR is highly conserved between virus isolates in both primary sequence and predicted secondary structure. We cloned and sequenced the 5' regions (nt 18 of the 5'UTR to nt 15 of the core coding sequence) of HCV isolates representing the six major genotypes and subcloned these into a bicistronic, dual luciferase reporter construct. The relative expression of the two luciferases, one directed by the HCV IRES and the other by cap- dependent ribosome scanning, was used to compare the activities of the different IRES elements in transfected cells. The 5'UTR from a genotype 2b isolate was the most efficient at directing translation in all four cell lines tested: BHK-21, HeLa-T4+, HuH7 and HepG2. In HepG2 cells the 2b 5'UTR was three times as efficient as the type 6a 5'UTR, which was generally the least active IRES tested. These data suggest that HCV isolates are not able to translate their ORF with equal efficiency, and provide a starting point from which further sequence-function studies can be undertaken.