Accelerated evolution in the protein-coding region of galectin cdnas, congerin I and congerin II, from skin mucus of conger eel (conger myriaster)

Two cDNAs encoding galectins named congerins I and II from the skin mucus of conger eel (Conger myriaster) were isolated and sequenced. Comparison of the nucleotide sequences of congerins I and II showed that the sequence similarities of the 5′ and 3′ untranslated regions (86 and 88%, respectively) were much higher than those of the protein-coding region (73%). The numbers of nucleotide substitutions per site (K_N) for the untranslated regions are smaller than the numbers of nucleotide substitutions per synonymous site (K_S) for the protein coding region. Furthermore, nonsynonymous nucleotide substitutions have accelerated more frequently than synonymous nucleotide substitutions in the protein coding region (K_A/K_S=2.57). These results suggest that accelerated substitutions have occurred in the protein-coding regions of galectin genes to generate diverse galectins with different molecular properties. Northern blot analysis showed that both congerins were expressed not only in the skin tissues but also in the stomach of conger eel.