Molecular characterisation of the 3′-end of the astrovirus genome

We have sequenced the 3′-end of the RNA genomes of 14 serotyped and 12 untyped isolates of human astrovirus. The sequences, which include all 8 serotypes, were used to predict secondary structures, postulate possible functional domains, reveal conserved regions suitable for nucleic acid amplification and perform phylogenetic analysis. The final nucleotides of the capsid protein precursor gene and the adjacent 3′-noncoding region were highly conserved and, except for 35 nucleotides with homology to a sequence in the 3′-end of a coronavirus RNA genome, unique to astrovirus family. This confirms that the 3′-end is a suitable target for universal and specific detection of astrovirus RNA. For the deduced 72 C-terminal amino acids of the capsid protein precursor, distances between the serotypes were found to vary from 0.1 substitution per site between serotypes 3 and 7 to more than one substitution per site between serotype 4 and the other serotypes. Different isolates of the same serotype were closely related, which indicates that the presently used typespecific antibodies differentiate between phylogenetically distinct groups. RNA secondary structures with minimal free energy were predicted using computer programs. Comparative sequence analysis verified the significance of certain of the predicted structural elements.