Nucleotide Sequence and Organization of Eight 3′ Open Reading Frames of the Citrus Tristeza Closterovirus Genome

The citrus tristeza closterovirus (CTV) RNA genome was cloned as cDNA generated from both CTV-specific doublestranded RNA and genomic RNA, and the sequence of the 3′ 7292 nucleotides was determined. The sequenced portion contained eight open reading frames potentially encoding, in the 5′ to 3′ direction, proteins with the apparent molecular weights of 65, 61, 27, 25 (capsid protein, CP), 18, 13, 20, and 23 kDa, and a potential noncoding region of 277 nucleotides. The 65-kDa protein is a viral homolog of cellular hsp70 heat shock proteins (hsp), the 61-kDa protein is distantly related to the hsp90 proteins, and the 27-kDa protein is a diverged copy of the CP. Database searches did not identify any protein sequences of significant similarity to the remaining four ORFs downstream of the CP. A specific four-gene module consisting of the hsp70 protein, the hsp90-related protein, the diverged copy of the CP, and the CP itself was found to be common in organization between CTV and beet yellows closterovirus. All four proteins in this module were highly conserved, indicating that these viruses probably have evolved from a common ancestor.