Isolation and Sequence Analysis of Bovine asl-Casein

Poly(A+) RNAwas isolated from lactating cow mammary gland and CDNAwas synthesized by a method which resulted in a high yield of products containing complete 5'-terminal mRNAsequences. Transformants were screened with a HaelU-EcoRl fragment for bovine asl-casein CDNA[M. Maki, M. Nagao, M. Hirose and H. Chiba, Agric. Biol Chem., 41, 441 (1983)]. A CDNAclone was isolated that contained the full length of asl-casein mRNAand its nucleotide sequence was determined. The amino acid sequence predicted from the nucleotide sequence was in good agreement with that determined with the purified mature asl-casein. The signal peptide consist-ing of 15 amino acids was identical to that of ovine asl-casein. High homology at the nucleotide sequence level in the signal peptide region and in the 5'-untranslated region was found between rat a-casein and bovine asl-casein.