Sequence of rat α– and γ–casein mRNAs: evolutionary comparison o the calcium–dependent rat casein multigene family

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Abstract
The complete sequences of rat α– and γ– casein mRNAs have been determined. The 1402-nucleotide α– and 864– nucleotide γ-casein mRNAs both encode 15 amino acid signal peptides and mature proteins of 269 and 164 residues, respectively. Considerable homology between the 5 1 non–coding regions, and the regions encoding the signal peptides and the phosphorylation sites, in these mRNAs as compared to several other rodent casein mRNAs, was observed. Significant homology was also detected between rat α– and bovine α sl – casein. Comparison of the rodent and bovine sequences suggests that the caseins evolved at about the time of the appearance of the primitive mammals. This may have occurred by intragenic duplication of a nucleotide sequence encoding a primitive phosphorylationsite, –(Ser),–Glu–Glu–, and intergenic duplication resulting in the small casein multigene family. A unique feature of the rat α– casein sequence is an insertion in the coding region containing 10 repeated elements of 18 nucleotides each. This insertion appears to have occurred 7–12 million years ago, just prior to the divergence of rat and mouse.