[Structure characteristics of ORF2a gene of potato leafroll virus Chinese isolate].

According to the genomic sequence of foreign four PLRV isolates, three pairs of specific primer were designed and synthesized. The cDNA of the ORF2a gene of PLRV-Ch was synthesized by reverse transcription and followed by Polymerase Chain Reaction amplication. The synthesized 3' and 5' cDNA fragment of the PLRV-Ch ORF2a gene were inserted into pUC19 and cloned in E. coli JM109 and were sequenced respectively. The middle cDNA fragment were directly sequenced. The homology of nucleotide sequence of PLRV-Ch compared with PLRV-S (Scotland, UK), PLRV-N(Netherlands), PLRV-A(Australia) and PLRV-C(Canada) were 98.96%, 98.70%, 94.79%, 97.5%, the homology of putative amino acid sequence are 97.97%, 97.97%, 89.69%, 95.94%. In 3' region of ORF2a gene a slippery sequence for-1 frameshift and its downstream "stem-loop" or "pseudoknot" and upstream nucleotide sequence repeats were found. Authors suggested that the nucleotide repeat sequences characteristic for PLRV could form a tight successively folded complementary double stranded regions and hairpins. This structure possibly has something to do with-1 frameshift. The amino acid sequence of C terminus region of 70 kD protein translated by motif IV has a protease characteristic motif and a helicase motif IV. The amino acid sequence of polypeptide translated by ORF2a gene undergoing frameshift has a single-stranded nucleic acid binding protein-like characteristic motif.