MOLECULAR-CLONING, SEQUENCING, AND EXPRESSION IN ESCHERICHIA-COLI OF THE POTATO VIRUS-Y CYTOPLASMIC INCLUSION GENE

Complete nucleotide sequences of cytoplasmic inclusion (CI) genes of two strains of potato virus Y (PVY) were determined from six polymerase chain reaction (PCR)-amplified cDNA clones. The size of the CI genes of both ordinary (PVY-0) and necrotic strains (PVY-T13) was 1902 nucleotides, with a sequence homology of 83.4%. Comparison of the predicted amino acid sequences showed more than 90% homology. When these were compared with those of other potyviruses, the homology ranged from 53 to 61%. cDNAs of all or a part of the PVY-OCI gene containing an additional initiation codon (ATG) at the 5' end and a stop codon at the 3' end were constructed by PCR amplification and cloned into an Escherichia coli expression vector, pKK 223-3. Complete and truncated PVY-OCI proteins were successfully produced in E. coli as judged by reactivities with PVY-OCI protein-specific antiserum. To our knowledge, this is the first report on expression of PVY CI proteins in E. coli.