Isolation and characterization of the bovine k‐casein gene

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Abstract
The bovine k‐casein gene has been isolated as a series of overlapping λ clones and shown to consist of five exons distributed over a total length of approximately 13 kb. Most of the mature protein‐coding sequence is contained in a single large exon. Approximately 65% of the gene has been sequenced together with portions of the 5′‐ and 3′‐flanking sequences. The immediate 5′‐flanking sequence contains several motifs which are characteristic of upstream regions including a TATA box, a CAAT box, a sequence similar to that recognized by transcription factor AP‐1 and a purine‐rich sequence resembling that found upstream in all other lactoprotein genes. Other possible regulatory sequences are found upstream of exon 4. The organization of the k‐casein gene, together with its upstream sequence, confirms previous conclusions that it is unrelated to the calcium‐sensitive‐casein gene familiy to which it is linked. Evidence is presented which supports a previous suggestion that k‐casein and the fibrinogens are evolutionarily related. Intron sequences contain several examples of the A family of the artiodactyl Alu‐like repeated sequences, together with a single example of a C‐family sequence. The remainders of the introns of the k‐casein gene, compared with the repeat elements and exons, are A + T‐rich. Among the Δ clones isolated, representatives were found of the A and B genetic variants which can be distinguished by restriction‐enzyme analysis. Several other examples of polymorphisms in the non‐coding region were found.

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