Human enteroviruses consist of more than 60 serotypes, reflecting a wide range of evolutionary divergence. They have been genetically classified into four clusters on the basis of sequence homology in the coding region of the single-stranded RNA genome. To explore further the genetic relationships between human enteroviruses and to characterize the evolutionary mechanisms responsible for variation, previously sequenced genomes were subjected to detailed comparison. Bootstrap and genetic similarity analyses were used to systematically scan the alignments of complete genomic sequences. Bootstrap analysis provided evidence from an early recombination event at the junction of the 5′ noncoding and coding regions of the progenitors of the current clusters. Analysis within the genetic clusters indicated that enterovirus prototype strains include intraspecies recombinants. Recombination breakpoints were detected in all genomic regions except the capsid protein coding region. Our results suggest that recombination is a significant and relatively frequent mechanism in the evolution of enterovirus genomes.

The RGD motif is exposed and flexible in common with other known integrin ligands. Although CAV9 resembles coxsackie B viruses (CBVs), several substitutions in the areas implicated in CBV receptor attachment suggest it may recognise a different receptor. The structure along the fivefold axis provides new information on the uncoating mechanism of enteroviruses. CAV9 might bind a larger natural pocket factor than other picornaviruses, an observation of particular relevance to the design of new antiviral compounds.

Genetic relationships between 35 clinical isolates of coxsackievirus A9 (CAV9),

In order to determine the overall molecular heterogeneity of echoviruses (EVs) we performed a genetic analysis of the prototype strains. Nucleotide and derived amino acid sequences from different genomic regions (5'UTR, capsid protein-coding and 3D polymerase genes) were used for molecular comparisons. On the basis of a comparison of partial amino acid sequences from the capsid protein VP2, all the sequenced EVs excluding EV22 and EV23 form a single cluster which is genetically homogeneous. All previously sequenced coxsackie B viruses (CBVs) and coxsackievirus A9 also belong to this same genetic cluster. Similar results were obtained when the 5'UTR or 3D polymerase gene sequences were used in comparisons. When amino acid sequences of the major capsid proteins of EV1 and EV16 were compared to those of previously sequenced enteroviruses, the length of the loops connecting the flsheets appeared to be relatively constant in the EV/CBV cluster. It can be concluded that EVs and CBVs have diverged relatively late in evolution.

Genomic regions responsible for the different tissue tropisms of coxsackievirus A9 (CAV9) and coxsackievirus B3 (CBV3) in newborn mice were investigated using recombinant viruses. Infectious cDNA clones of CAV9, a virus known to infect striated muscle, and CBV3, affecting the central nervous system, pancreas, liver, brown fat and striated muscle, were used to generate chimeric viruses. In situ hybridization analysis of different tissues from mice infected with the recombinant viruses, constructed by exchanging the 5h non-coding region (5hNCR), structural and nonstructural genes, demonstrated that the pancreo-and liver tropism map predominantly to CBV3 sequences within the capsid genes, evidently due to receptor recognition. Although the major neurotropism determinant in the CBV3 genome was in the capsid region, viruses containing the CAV9 capsid were also able to initiate infection in the central nervous system provided they contained the CBV3 5hNCR. The presence of the 5hNCR of CAV9 clearly enhanced muscle tissue tropism.