The complete genome sequence, organization and affinities of carrot red leaf virus

A sequence of 5723 nucleotides (GenBank accession number: AY695933) is reported for the RNA genome of an isolate of Carrot red leaf virus (CtRLV). The sequence is predicted to contain six large open reading frames and non coding sequences of 28 nucleotides at the 5′ end, 110 nucleotides at the 3′ end, and 215 nucleotides between the two main blocks of coding sequences. The 5′ coding region encodes two polypeptides with calculated molecular masses (Mr) of 28.6 kDa (P0) and 68.2 kDa (P1) that overlap in different reading frames. Circumstantially, the third ORF in the 5′ block is putatively translated by frameshift read-through to yield a polypeptide (P1 + P2) with a calculated Mr of 116.9 kDa. Frameshifting is predicted at a “shifty” sequence (GGGAAAC; nt 1523–1529) also found in most members of the genus Polerovirus. The C-terminal region of the 116.9 kDa polypeptide includes the consensus sequence for the viral RNA-directed RNA polymerase. The 3′ block of coding sequence defines three putative polypeptides of: 23.0 kDa (P3), 21.3 kDa (P4, in a different reading frame) and 77.2 kDa (P3 + P5, by read-through of P3) respectively. From the genome structure of CtRLV, it is suggested that this virus belongs to the genus Polerovirus, rather than either the genus Luteovirus or the genus Enamovirus.