The complete genome sequence of the major component of a mild citrus tristeza virus isolate

The genome of the Spanish mild isolate T385 of citrus tristeza virus (CTV) was completely sequenced and compared with the genomes of the severe isolat es T36 (Florida), VT (Israel) and SY568 (California), The genome of T385 wa s 19259 nt in length, 37 nt shorter than the genome of T36, and 33 and 10 n t longer than those of VT and SY568, respectively, but their organization w as identical, T385 had mean nucleotide identities of 81.3, 89.3 and 94% wit h T36, VT and SY568, respectively. The 3' UTR had over 97% identity in all isolates, whereas the 5' UTR of T385 had 67% identity with VT, 66.3% with S Y568 and only 42.5% with T36, In the ceding regions, the nucleotide differe nces between T385 and VT were evenly distributed along the genome (around 9 0% identity); this was not observed between T385 and the other isolates. T3 85 and T36 had nucleotide identities around 90% in the eight 3'-terminal OR Fs of the genome, but only 72.3% in ORF 1a, a divergence pattern similar to that reported previously for T36 and VT. T385 and SY568 had nucleotide ide ntities close to 90% in the 5'- and 3'-terminal regions of the genome, wher eas the central region had over 99% identity. Our data suggest that the cen tral region in the SY568 genome results from RNA recombination between two CTV genomes, one of which was almost identical to T385.