Rosner, A., Virology Department, ARO, The Volcani Center, Bet Dagan 50250, Israel
Maslenin, L., Virology Department, ARO, The Volcani Center, Bet Dagan 50250, Israel

Potato isolates of Potato virus Y (PVY) were divided into two major groups based on nucleotide sequence homology in the 5'-end region of their genomes. Several characteristic nucleotide modifications differentiated the two virus groups. Sequence similarity within members of each group was 89-100%, whereas between members of the respective groups there was sequence divergence of up to 33%. The two groups were distinguished by restriction cleavage of the virus PCR products elicited by group-specific restriction endonucleases: Xho II and Nsp I (group I) and Mbo II, Fok I and Nco I (group II). The sites of the first three enzymes (group I-specific) were sequentially positioned so that a sequence of 16 nucleotides preceding the ATG codon could be determined in this way. Group I included members of the tobacco necrotic (N) and non-necrotic (O) strains of PVY, whereas the potato tuber necrotic isolate NTN-H belonged to the second group, which included also non-tuber and tobacco leaf necrotic members. It seems therefore that the biological characteristics of the tuber or tobacco leaf necrosis are not related to nucleotide modifications at the 5'-UTR but rather to group-specific differences.