cDNA and amino acid sequences of rainbow trout (Oncorhynchus mykiss) lysozymes and their implications for the evolution of lysozyme and lactalbumin
The complete 129-amino-acid sequences of two rainbow trout lysozymes (I and II) isolated from kidney were established using protein chemistry microtechniques. The two sequences differ only at position 86, I having aspartic acid and II having alanine. A cDNA clone coding for rainbow trout lysozyme was isolated from a cDNA library made from liver mRNA. Sequencing of the cloned cDNA insert, which was 1 kb in length, revealed a 432-bp open reading frame encoding an amino-terminal peptide of 15 amino acids and a mature enzyme of 129 amino acids identical in sequence to II. Forms I and II from kidney and liver were also analyzed using enzymatic amplification via PCR and direct sequencing; both organs contain mRNA encoding the two lysozymes. Evolutionary trees relating DNA sequences coding for lysozymesc and α-lactalbumins provide evidence that the gene duplication giving rise to conventional vertebrate lysozymesc and to lactalbumin preceded the divergence of fishes and tetrapods about 400 Myr ago. Evolutionary analysis also suggests that amino acid replacements may have accumulated more slowly on the lineage leading to fish lysozyme than on those leading to mammal and bird lysozymes.
Key wordsConventional lysozymes Calciumbinding lysozymes Gene duplications Tetrapods Insects Evolutionary trees Statistical testing Replacement mutations Base composition PCR
150 mM sodium chloride, 15 mM sodium citrate pH 7.0
polymerase chain reaction
Unable to display preview. Download preview PDF.
- Maniatis T, Fritsch EF, Sambrook J (1982) Molecular cloning. A laboratory manual. Cold Spring Harbor Laboratory, Cold Spring Harbor NYGoogle Scholar
- Rodríguez R, Menéndez-Arias L, González de Buitrago G, Gavilanes JG (1987) Structure of the pigeon lysozyme and its relationship with other typec lysozymes. Comp Biochem Physiol 88B:791–796Google Scholar
- Romer AS (1966) Vertebrate paleontology, ed 3. University of Chicago Press, Chicago ILGoogle Scholar