Molecular genetics and evolution of stomach and nonstomach lysozymes in the hoatzin.

Multiple genes of the hoatzin encoding stomach lysozyme c and closely related members of this calcium-binding lysozyme c group were cloned from a genomic DNA library and sequenced. There are a minimum of five genes represented among these sequences that encode two distinct groups of protein sequences. One group of three genes corresponds to the stomach lysozyme amino acid sequences, and the remaining genes encode predicted proteins that are more basic in character and share several sequence identities with the pigeon egg-white lysozyme rather than with the hoatzin stomach lysozymes. Despite these structural similarities between some of the hoatzin gene products and the pigeon lysozyme, phylogenetic analyses indicate that all of the hoatzin sequences are closely related to one another. This is borne out by the relatively small genetic distances even in the intronic regions, which are not subject to the selective pressures operating on the coding regions of the stomach lysozymes. These results suggest that multiple gene duplication events have occurred during the evolution of hoatzin lysozymes.