Expression of two different endogenous galactoside-binding lectins sharing sequence homology.

The endogenous beta-D-galactoside-binding lectins of UV-2237-IP3 fibrosarcoma cells consist of two polypeptides with molecular weights of 14,500 (L-14.5) and 34,000 (L-34). Recently we constructed complementary DNA (cDNA) libraries from these cells in the expression vector lambda gt11 and isolated and characterized cDNA clones encoding the two lectin species (A. Raz et al., Exp. Cell Res., 173: 109, 1987). We report here on the similarity in structure and gene number in genomic DNA of the fibrosarcoma cells and syngeneic normal mouse lung DNA. The expression of mRNAs hybridizing to these cDNAs was evaluated in three pairs of normal versus their transformed cell variants. Messenger RNA corresponding to the Mr 34,000 lectin was present more abundantly in the transformed cells than in their normal counterparts, while no difference was detected between the cell pairs with respect to mRNA levels corresponding to the Mr 14,500 lectin. We have established the nucleotide sequences of the two cDNA clones. The deduced amino acid sequence of L-14.5 lectin cDNA clone (L-3) is significantly homologous to the sequence of six other L-14 vertebrate galactoside binding lectins. The sequence of the Mr 34,000 lectin cDNA clone (M5) revealed that it shares a stretch of 39 amino acids with all of the L-14 galactoside binding lectins, irrespective of origin of the species, suggesting both that they are all derived from a common ancestral gene, and that this domain is necessary for similar sugar binding properties.