Hepatitis C virus (HCV) shows substantial nucleotide sequence diversity distributed throughout the viral genome, with many variants showing only 68 to 79 % overall sequence similarity to one another. Phylogenetic analysis ofnucleofide sequences derived from part of the gene encoding a non-structural protein (NS-5) has provided evidence for six major genotypes of HCV amongst a worldwide collection of 76 samples from HCV-infected blood donors and patients with chronic hepatitis. Many of these HCV types comprised a number of more closely related subtypes, leading to a current total of 11 genetically distinct viral populations. Phylogenetic analysis of other regions of the viral genome produced relationships between published sequences equivalent to those found in NS-5, apart from the more highly conserved 5' non-coding region in which only the six major HCV types, but not subtypes, could be differentiated. A new nomenclature for HCV variants is proposed in this communication that reflects the twotiered nature of sequence differences between different viral isolates. The scheme classifies all known HCV variants to date, and describes criteria that would enable new variants to be assigned within the classification as they are discovered.

We are researchers who have published analyses of nucleic acid sequence variation of hepatitis C virus (HCV) and associated virological and clinical significance. We are concerned that our investigations are hampered by the lack of a consensus nomenclature for variants of HCV and that this leads to confusion when results from different laboratories are compared. Furthermore, because there are no consistently applied criteria by which new genotypes are defined, investigators assign new type descriptions to novel sequence variants on an ad hoc basis without agreement from

We have determined the nucleotide sequence at the extreme 5' and 3' termini of the hepatitis C virus (HCV) genome. Our analyses ofthese sequences show (t) the nucleotide sequence in the 5' untranslated region is highly conserved among HCV isolates of widely varying geographical orign, (i) within this region, there are blocks of nucleotide sequence homology with pestiviruses but not with other viruses, (ii) the relative position of short open reading frames present in the same region of the HCV genome is similar to that of the pestiviral genome, (iv) RNAs truncated at the 5' and 3' ends are found, but the origin and functions of these RNAs are unknown, and (v) poly(A) tails appear to be present on 3' subgenomic RNAs. (ORFs). The HCV genome, however, displays singular characteristics at each terminus. We detect a hairpin structure at the 5' end of the genome as well as 5' and 3' subgenomic RNAs, the latter of which are polyadenylylated. These are consistent with a polyadenylylated 3' terminus of the viral genome and perhaps of functional subgenomic RNAs. Our data provide insights into the organization of the HCV genome, which may have important ramifications regarding the replication strategy and evolution of the virus. MATERIALS AND METHODSRNA was extracted from a high-titer plasma of an experimentally infected chimpanzee (6) and plasma (or serum) from HCV-positive or negative blood donors by a low-temperature guanidinium thiocyanate method (7). Poly(A)+ RNA was isolated from the liver ofthe same infected chimpanzee by the guanidinium thiocyanate/urea method (8). cDNA was synthesized from RNA according to Han and Rutter (9) and amplified by polymerase chain reaction (PCR) according to Saiki et al. (10). Briefly, RNA isolated from about 500 Al of plasma or S Ag of poly(A)+ liver RNA was converted into single-stranded cDNA by reverse transcriptase (BRL) using 150 pmol of the appropriate cDNA primer. For 5' end characterization by primer extension (7), first-strand cDNA was precipitated by spermine (11) and tailed with dA (9). Tailed or untailed cDNA was converted into double-stranded cDNA using a second-strand cDNA primer (9). This doublestranded cDNA was amplified using the indicated HCVspecific PCR primers for 35 cycles (940C, 1.5 min; 60'C, 2 min; 720C, 3 min). PCR without cDNA template was routinely performed to check for possible contamination during PCR. The PCR product was analyzed by Southern blot hybridization using a 32P-labeled oligonucleotide probe. The sequences and locations in the HCV genome of various cDNA and PCR primers are shown in Figs. 2 and 5. Most primers were designed to contain a Not I site for subsequent cloning of the PCR products into pUC18S, which contains a polylinker derived from Agt22 (9). DNA sequence was obtained by the supercoil sequencing (12) or the direct PCR sequencing method (13). RESULTSBased on the sequence of the major part of the HCV genome determined from overlapping A clones (2), we devised a directed strategy for obtaining clones representing the remaini...

Rapid isothermal nucleic acid amplification technologies can enable diagnosis of human pathogens and genetic variations in a simple, inexpensive, user-friendly format. The isothermal exponential amplification reaction (EXPAR) efficiently amplifies short oligonucleotides called triggers in less than 10 min by means of thermostable polymerase and nicking endonuclease activities. We recently demonstrated that this reaction can be coupled with upstream generation of trigger oligonucleotides from a genomic target sequence, and with downstream visual detection using DNA-functionalized gold nanospheres. The utility of EXPAR in clinical diagnostics is, however, limited by a nonspecific background amplification phenomenon, which is further investigated in this report. We found that nonspecific background amplification includes an early phase and a late phase. Observations related to late phase background amplification are in general agreement with literature reports of ab initio DNA synthesis. Early phase background amplification, which limits the sensitivity of EXPAR, differs however from previous reports of nonspecific DNA synthesis. It is observable in the presence of single-stranded oligonucleotides following the EXPAR template design rules and generates the trigger sequence expected for the EXPAR template present in the reaction. It appears to require interaction between the DNA polymerase and the single-stranded EXPAR template. Early phase background amplification can be suppressed or eliminated by physically separating the template and polymerase until the final reaction temperature has been reached, thereby enabling detection of attomolar starting trigger concentrations.