Antifreeze Glycoproteins of Two Unrelated Polar Fishes: Gene Structure, Organization and Evolution

Abstract

The AFGPs of the northern cods are also encoded by a family of polyprotein genes in which multiple AFGP coding sequences linked in tandem by small cleavable spacers Args or Arg-Ala-Ala-Arg's. However, the northern cod AFGP genes show no sequence identity with trypsinogen gene, indicating trypsinogen gene is not the progenitor of this group of AFGP genes. The southern and northern AFGP genes also have different signal peptides, different intron-exon organizations, different spacer sequences thus are the processing of the polyprotein precursors, and drastically different codon patterns for the repetitive AFGP coding sequence. This molecular evidence in conjunction with paleontological and paleoclimatic data indicate the near-identical AFGPs of Antarctic notothenioids and northern cods evolved independently.