Cloning and molecular characterization of a yak α-lactalbumin cDNA from mammary tissue

α-Lactalbumin is a calcium-binding protein, and is present in all mammalian milks. It plays an important role in regulating the biosynthesis of lactose in mammary gland. In the present work, we have cloned and characterized the full-length open reading frame of yak α-lactalbumin cDNA from mammary tissue. The cDNA were synthesized by RT-PCR technique, then cloned using the pMD18-T Vector, and sequenced. The sequence analysis indicated that the obtained cDNA of 478-bp spanned an open reading frame of 429-bp which predicted a precursor protein of 142 amino acids with a signal peptide of 19 amino acids. Compared with the corresponding sequences in GenBank of yak, cattle, buffalo, sheep, goat, pig, and rabbit, the yak α-lactalbumin sequence obtained from this study had identity of 74.13 to 99.77% in cDNA, and identity of 59.86 to 100.00% and similarity of 75.35 to 100.00% in deduced amino acids, indicating a high homology with other species. The phylogenetic tree based on α-lactalbumin cDNA sequences indicated that yak α-lactalbumin were closely related to its cattle counterpart, and this clustering is generally in accordance with the classic taxonomic relationship.