Similarity of the nucleotide sequences of rat alpha-lactalbumin and chicken lysozyme genes.

alpha-Lactalbumin (alpha-LA) is a milk protein that interacts with the enzyme galactosyltransferase, modifying its substrate specificity in a way which promotes the transfer of galactose to glucose, resulting in a way which promotes the transfer of galactose to glucose, resulting in a beta-1----4 glycosidic linkage and the synthesis of lactose. Lysozyme, an enzyme which catalyses the hydrolysis of a beta-1----4 glycosidic linkage in polysaccharides, has been shown to be structurally related to alpha-LA and it has been proposed that they have arisen from a common ancestral gene. To compare their evolutionary relationships, we report here the complete nucleotide sequence of the rat alpha-LA gene, including its 5'-flanking sequences, and compare its gene structure with the chicken egg-white lysozyme gene. Both genes contain three introns at similar positions. The first three exons of the two genes have similar nucleotide sequences. The fourth exon of alpha-LA, which partly codes for the C-terminal residues of the protein, essential for its interaction with galactosyltransferase, is markedly different from the corresponding exon of the lysozyme gene and is preceded by two (TG)n repeats.