1. The bovine ti-casein gene has been isolated as a series of overlapping I 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.2. 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 4.3. 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 ic-casein and the fibrinogens are evolutionarily related.4. 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 rc-casein gene, compared with the repeat elements and exons, are A + T-rich.5. Among the I 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.The caseins are the predominant proteins in the milk of most species. As well as being the main source of amino acids for the suckling infant, the caseins serve to raise the calcium and phosphate concentrations in milk to levels well in excess of the solubility product of calcium phosphate by forming loosely ordered aggregates, termed micelles, which sequester calcium phosphate. Bone formation in the young animal thus depends on the ability of casein to transport appropriate quantities of calcium phosphate in milk.In bovine milk more than 20 individual components can be resolved when whole casein is analyzed electrophoretically under dissociating conditions [I]. These result from posttranslational modification and genetic variation of four primary translation products which correspond to asl-, clS2-, pand k--caseins. The xsl-, xs2-and p-caseins are insoluble in the presence of calcium ion at the concentrations at which it occurs in milk and these caseins are referred to as the calciumsensitive caseins. In contrast, K-casein is insensitive to the presence of calcium and is referred to as the micelle stabilizer because it is essential for the formation of stable casein micelles [2]. Following ingestion, the caseins are immobilized in the stomach as a result of clot formation. This occurs when chymosin (rennin) or pepsin specifically cleaves a single PheMet bond in K-casein to form insoluble para-K-casein (105 residues) and a soluble macropeptide containing the C-termind 64 amino acid residues of ...

Several IgE heavy (H) chain transcripts are produced by alternative splicing between constant region (CH3 and CH4) and membrane (M1 and M2) exons and by differential cleavage-polyadenylation at poly(A) sites downstream of the CH4 and M2 exons. We have now characterized the poly(A) signal of the epsilon transcripts that contain membrane exon sequences (epsilon CH4-M1'-M2, epsilon CH4-M1-M2, epsilon CH4-M2' and epsilon CH4-M2") and have determined the complete sequence of the M2 exon and 1.4 kb of downstream genomic DNA. The membrane locus poly(A) site was identified by RACE-PCR analysis of epsilon transcripts obtained from IgE-producing myeloma cells and normal peripheral blood lymphocytes (PBL). All membrane exon transcripts were found to be polyadenylated following a CA dinucleotide located 1046 nt from the beginning of the M2 exon. An AGTAAA hexamer, located 13 nt upstream from the site of cleavage and polyadenylation, was the only poly(A) signal sequence present in the 1.4 kb of genomic DNA downstream of the M2 exon. A (G+T)-rich region, which is also conserved in most poly(A) signals, was present 50 nt downstream of the AGTAAA hexamer. Northern blot analysis confirmed that this poly(A) site is used by the membrane exon epsilon mRNAs expressed by the U266 myeloma. The four membrane exon transcripts were detected in different relative amounts in PBL and IgE-producing myeloma cells, which could reflect different epsilon mRNA splicing patterns during B-cell differentiation.

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