cDNA cloning and sequence analysis of the lectin genes of the Korean mistletoe (Viscum album coloratum)

We previously isolated a lectin of the Korean mistletoe (Viscum album color atum) [Yoon et al. (1999)]. The cDNA clones that encode the A- or the B-cha in of the Korean mistletoe lectin were cloned by reverse transcriptase poly merase chain reaction (RT-PCR). The mRNAs that were extracted from the Kore an mistletoe were amplified, ligated into the pGEM-T easy vector, and scree ned with a Korean mistletoe lectin-specific probe. The probe was prepared b y PCR amplification of the Korean mistletoe DNA using a primer set designed on the basis of amino acid sequences of the Korean mistletoe lectin that w e had purified and reported. Unlike a recent report, which states that the European mistletoe lectin gen e has no isoforms, several different clones of the A- and B-chains of the K orean mistletoe lectin were cloned from the same primer set. Three clones o f each were selected for sequencing. The sizes of the A-chains were 762, 76 2, and 768 bp, respectively. The B-chain sizes were 798, 789, and 789 bp, r espectively. Each of the clones showed significant variation in the amino a cids sequence, including the N-linked glycosylation sites of the lectin. Th e sequence analysis of each of the Korean lectin clones, in comparison with the European mistletoe lectin and the other type II ribosome binding prote ins, is discussed in the text. In addition, Southern blot analysis of the K orean mistletoe genomic DNA, restricted by different enzymes and hybridized with the lectin DNA, showed multi-bands, supporting the existence of multi copy genes or a gene family. These data suggest that heterogeneity of the mistletoe lectin is not only i ntroduced by post-translational modifications, but also by expression of is otypes of the lectin genes.