3'-TERMINAL SEQUENCE OF THE PLUM POX VIRUS PS AND O6 ISOLATES - EVIDENCE FOR RNA RECOMBINATION WITHIN THE POTYVIRUS GROUP

The sequence of the 3'-terminal 1768 nucleotides of the PS and 66 isolates of plum pox virus (PPV) has been determined and compared with that of the equivalent regions of other PPV isolates sequenced previously. The sequenced region is part of the PPV open reading frame encoding the last 186 amino acids of the NIb protein and the coat protein (CP, 330 amino acids), followed by a non-coding region of 220 nucleotides and a poly(A) tail. PPV-PS and PPV-66, just like PPV-E1 Amar, show rather high levels of nucleotide diversity in the sequence encoding the C-terminal region of the Nlb protein (19.4 to 31 %) and the N terminus of CP (22.8 to 41.1 %) when compared with PPV-Rankovic, PPV-D and PPV-NAT, whereas the level of diversity in the rest of the CP sequence and the 3' non-coding region is low (8 to 10-8 % and 5.5 to 7.7 %, respectively). However, the first 429 sequenced nucleotides of PPV-o6 are very similar to those of the PPV-Rankovic, PPV-D and PPV-NAT isolates, whereas the rest of the sequence clearly resembles PPV-PS. Thus, PPV-66 seems to be the result of a natural recombination event between two wild strains of PPV. To our knowledge this is the first evidence of homologous RNA recombination (a process which could play an important role in the evolution of RNA viruses) within the potyvirus group.