To survive the freezing marine environment, the Antarctic eel pout, Lycodichthys dearborni synthesizes high concentration of type III antifreeze proteins (AFP III). In the process of characterizing the various types of AFP III mRNA present in the L. dearboni liver, a 2.87 kb mRNA encodes for multiple domains of AFP III was identified. This cDNA encodes 12 tandemly repeated segments, each translates into a 7 kD AFP III molecule plus a 9-amino acid linker. This naturally occurred and functional multimer type III antifreeze protein gene is the first of this kind being identified. The organization strongly mimics the polyprotein structure found in the genes for another type of bio-antifreezes, the antifreeze glycoprotein, AFGP. The AFP III and AFGP are compositionally and structurally completely different, and synthesized by fishes in different suborders. The presence of the similar polyprotein structures in the different types of antifreeze genes may imply a common organizational mechanism in the fish genomes for adapting to the extremely cold polar environment.