Molecular characterization of the 5' non-coding region of South African GBV-C/HGV isolates: major deletion and evidence for a fourth genotype.

GB virus C/hepatitis G virus (GBV-C/HGV) has been characterised as a novel flavivirus, and to date three known genotypes have been cloned. Greater genetic variation of GBV-C/HGV has been demonstrated in West African isolates, but no major deletions have been shown in the 5' non-coding region (NCR). The 5'NCR regulates protein translation via an internal ribosomal entry site (IRES). We cloned, sequenced, and analysed a 344-bp polymerase chain reaction (PCR) product, representing >60% of the 5'NCR, from 32 GBV-C/HGV PCR-positive volunteers. Wild-type virus amplicons were detected in all samples. However, 5/32 (15.6%) also amplified another fragment of between 205 and 231 bp. Sequence analysis showed all cloned PCR fragments to be GBV-C/HGV-specific. A typical deletion of 113-131 bp with minor variation was detected in isolates generating the smaller bands. RNA secondary structure analysis showed the deletions to be over domains II and III. This finding suggests that nucleotides 303-444 may be non-essential for 5'NCR functioning. Phylogenetic analysis demonstrated a novel fourth South African genotype, distinct from genotypes 1-3 with DNA distances of >0.1000. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) values for the wild-type and mutant samples were normal. This study documents the first major deletion in the 5'NCR of GBV-C/HGV, and suggests that bases 303-444 may not be essential for viral replication and ribosomal entry. A fourth GBV-C/HGV genotype appears to predominate in South Africa.