The gene of chlamysin, a marine invertebrate-type lysozyme, is organized similar to vertebrate but different from invertebrate chicken-type lysozyme genes

In a recent publication we reported the protein purification, characterization, and the gene isolation of a cDNA encoding the antibacterial cold-active lysozyme-like protein chlamysin from the marine bivalve Chlamys islandica. A 4.2 kb genomic chlamysin gene has now been amplified and sequence-analyzed. By comparison to the cDNA sequence and its translation product, the coding region was found separated in four exons of 38-252 bp. The introns range in size from 0.8 to 1.5 kb, and have traditional spliceosomal intron 5'-GT donor and 3'-AG acceptor sites for splicing. Two of the introns contain multiple copies of three sequence motifs not found repeated in other published genes. The over-all gene organization of chlamysin resembles chicken-type (c-type) lysozyme genes in vertebrates, but is different from the three-exon structure in invertebrate c-type lysozyme genes. A phylogenetic analysis of invertebrate-type (i-type) and c-type lysozyme proteins demonstrated a large evolutionary distance between the i-type and the c-type enzyme classes. Exons of the i-type genes are not equally organized according to their homolog protein domains.