Rat β casein cDNA: sequence analysis and evolutionary comparisons

Abstract

The complete sequence of a 1072 nucleotide rat β-casein cDNA insertion in the hybrid plasmid pCβ23 has been determined. Primer extension was employed to determine the sequence of an additional 82 5′-terminal nucleotides in β-casein mRNA. Rat β-casein mRNA consists of a 696 nucleotide coding region, flanked by 52 nucleotide 5′ and 406 nucleotide 3′ noncoding regions, including a 40 nucleotide poly(A) tail. The derived 216 amino acid sequence of rat β-casein was compared to the previously determined sequences of β-caseins from several other species. Approximately 38% of the amino acids have been conserved among the rat, ovine, bovine and human sequences and these conserved amino acids occurred in clusters throughout the protein. One such cluster containing the majority of the potential casein phosphorylation sites was located near the amino terminus. Contrary to the considerable divergence observed for the processed β-casein, 14 of 15 amino acids in the signal peptide sequence of the precasein ware identical between the rat and ovine caseins.