科研之友
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摘要
kappa-Casein is one of the major proteins in the milk of mammals. It plays an important role in determining the size and specific function of milk micelles. We have previously identified and characterized a genetic variant of yak kappa-casein by evaluating genomic DNA. Here, we isolate and characterize a yak kappa-casein cDNA harboring the full-length open reading frame (ORF) from lactating mammary gland. Total RNA was extracted from mammary tissue of lactating female yak, and the kappa-casein cDNA were synthesized by RT-PCR technique, then cloned and sequenced. The obtained cDNA of 660-bp contained an ORF sufficient to encode the entire amino acid sequence of kappa-casein precursor protein consisting of 190 amino acids with a signal peptide of 21 amino acids. Yak kappa-casein has a predicted molecular mass of 19,006.588 Da with a calculated isoelectric point of 7.245. Compared with the corresponding sequences in GenBank of cattle, buffalo, sheep, goat, Arabian camel, horse, and rabbit, yak kappa-casein sequence had identity of 64.76-98.78% in cDNA, and identity of 44.79-98.42% and similarity of 53.65-98.42% in deduced amino acids, revealing a high homology with the other livestock species. Based on kappa-casein cDNA sequences, the phylogenetic analysis indicated that yak kappa-casein had a close relationship with that of cattle. This work might be useful in the genetic engineering researches for yak kappa-casein.
