Isolation and characterization of the bovine k‐casein gene

Abstract

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 ...

Associação de SNPs nos genes para κ-caseína e β-lactoglobulina com curvas de lactação em cabras leiteiras

“…Os quatro genes da caseína estão mapeados no cromossomo 6, em cabras, enquanto os genes para α-lactalbumina e β-lactoglobulina foram mapeados no cromossomo 5 (Hayes et al, 1993). O gene da κ-caseína tem efeito positivo sobre a produção de proteína do leite e também é importante para a estrutura e a estabilidade das micelas de caseína, que aumentam o conteúdo de proteína total nos derivados do leite e a eficiência na produção de queijo (Alexander et al, 1988).…”

Caprine κ-Casein (CSN3) Polymorphism: New Developments in Molecular Knowledge

“…Therefore, the κ-casein gene (CSN3) is unlikely to be completely free of selective constraints (Ward et al, 1997). Interspecies comparisons have demonstrated that CSN3 possesses the highest degree of conservation among the casein genes, which may be related to its essential function as a stabilizer of casein micelles (Alexander et al, 1988). On the other hand, high intraspecies variability has been reported for CSN3 in cattle (for a review see Formaggioni et al, 1999) and, more recently, in goats.…”

Joint effects of CSN3 and LGB genotypes and their relation to breeding values of milk production parameters in Czech Fleckvieh

“…The kappa-casein gene is situated on bovine chromosome 6 and encodes milk protein important for the structure and stability of casein micelles (Alexander et al, 1988). Polymorphism of the kappa-casein gene has been known since 1964 (Neelin, 1964), and nine alleles are known in all.…”