Hepatitis C virus (HCV) is the main cause of parenteral non-A/non-B hepatitis and was the major agent causing post-transfusion hepatitis. Since its discovery in 1989 (Choo et al. 1989) many isolates have been sequenced. HCV consists of a heterogeneous mix of isolates defined by genotype; each of which is further classified into subtypes (Simmonds 1998). So far about six genotypes and more than 100 subtypes have been defined (Fig. 1). HCV has a positive single stranded RNA genome of about 9,500 nucleotides in length and shows similarities to the genome organization of flavi and pesti viruses. Its single open reading frame (Fig. 2) includes three structural proteins: core and the two glycolysated putative envelope proteins E1 and E2. Previous reports suggest that E1 and E2 interact and form a complex which has been proposed to be a functional subunit of HCV virions. From the six non structure proteins, the two protease NS2 and NS3 and the RNA dependent RNA polymerase NS5B have been characterized very well. The NS4A is an important cofactor for NS3 protease and seems to be important for the generation of replicative complexes within the infected cell. The c-terminal 456 amino acids of NS3 has in addition ATPase and RNA helicase activity. These activities have been suggested due to comparison of sequences to other helicases. The function of NS5A is not yet known. It can be found after expression in the periplasmatic membrane fraction of the nucleos and seems to be heavy phosphorylated. NS5A contained the sequence which is correlated to a sensitivity of HCV genotype 1b and interferon. NS5B contains a known amino acid sequence motive glycin, aspertate which is highly conserved in RNA dependent RNA polymerases. This gene product was early on thought to be the viral RNA polymerase of HCV. This has bee
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