MOLECULAR-CLONING AND HETEROGENEITY OF THE HUMAN HEPATITIS-C VIRUS (HCV) GENOME

The Japanese variant of the hepatitis C virus (HCV-N) genome, consisti ng of 9440 nucleotides in length, was cloned from a small amount (2 ml ) of plasma from a single Japanese carrier by using RT-PCR and modifie d RT-PCR. The HCV-N genome has a long open reading frame that encodes a 3014 amino acid polyprotein with 340 and 57 bases of 5' and 3' non-c oding sequences, respectively. HCV-N has a 4-amino-acid insertion in t he NS5 region as compared to other HCV isolates, but this insertion is found to be very rare upon direct sequencing of that region. Comparat ive sequence analysis of all the complete and partial HCV sequences th at were reported indicates that HCV can be subdivided into at least 4 groups. The HCV-N isolate has a high homology with HCV-J and HCV-BK (> 90%) and so belongs to group II, but shows less similarity to HCV-1 ( > 78%, group I) and least to HC-J6 (> 67%, group III). Among these HCV isolates, the 5' non-coding region was the most conserved (> 93%) sin ce it plays an important role in replication. The RT-PCR assay to dete ct HCV-RNA, using the primers deduced from this region, was very sensi tive and specific. The putative core protein could become an important target for immunoassay because of a high degree of amino acid sequenc e similarity in that region. A high degree of diversity and a low simi larity between each HCV isolate in the putative envelope protein play an important role in the chronicity of HCV infection and development o f immunopreventive agents, such as immunoglobulin and vaccine for that infection.