The 5' untranslated region of GB virus B shows functional similarity to the internal ribosome entry site of hepatitis C virus.

Since its characterization in 1995, there has been increasing interest in the significance of GB virus B (GBV-B) due to its close phylogenetic relationship to hepatitis C virus (HCV). The genome of GBV-B is similar in length and organization to that of HCV and the two viruses share sequence similarity in their 5' untranslated regions (5'UTR). A secondary structure model of the GBV-B 5'UTR has been proposed by comparative sequence analysis with HCV. The highly conserved secondary structure, present in HCV and the pestiviruses, is also present in the 5'UTR of GBV-B. Translation of the HCV polyprotein initiates via an internal ribosome entry site (IRES) and it is proposed that the GBV-B UTR may function in a similar manner. Dicistronic reporter constructs were made to investigate the function of the GBV-B 5'UTR. Mutational analysis and in vitro translation experiments demonstrate that GBV-B initiates translation via an IRES.