Nucleotide sequences of bovine alpha S1- and kappa-casein cDNAs

Expression of synthetic cDNA sequences encoding human insulin-like growth factor-1 (IGF-1) in the mammary gland of transgenic rabbits

We have developed an expression system where foreign proteins are synthesized specifically in the mammary gland of transgenic rabbits and secreted into the milk. Regulatory elements were isolated from the bovine alpha S1-casein-encoding gene and combined with a synthetic DNA coding for human IGF-1 and for [Gln58]IGF-1, an IGF-1 analogue. The resulting hybrid DNA constructs were used to generate transgenic rabbits. Females of seven transgenic lines tested were positive for synthesis of IGF-1. Transmission of the transgene to progeny and IGF-1 production in female offspring was observed in all transgenic lines analysed. As expected, expression of transgene mRNA could only be detected in the mammary gland. Production levels of transgenic protein were as high as 1 g IGF-1 per liter rabbit milk. IGF-1, as well as [Gln58]IGF-1, when secreted into rabbit milk, was correctly processed and biologically active. IGF-1 was purified from the milk of transgenic rabbits to a nearly homogenous active form.

Lysozyme-encoding bovine cDNAs from neutrophile granulocytes and mammary gland are derived from a different gene than stomach lysozymes

cDNA copies of a bovine lysozyme (bLys)-encoding gene (Lys) were isolated from libraries specific for granulocytes, as well as the lactating mammary gland. Analysis of each of the longest Lys-specific cDNA inserts revealed nucleotide sequence identity over the entire overlap of 1418 bp. Incomplete at the 5' end, the combined sequence codes for 11 of the 18-amino-acid (aa) Lys leader peptide and 130 aa residues of the mature Lys. Similar to mouse and human Lys from blood cells, the encoded protein contains one aa residue more (Pro103) than any of the bLys derived from stomach. Furthermore, unlike any of the known bLys genes, our sequence reveals the copy of a bovine retroposon element in the 3' untranslated region (UTR) of the mRNA approximately at the same position where an Alu-retroposon element resides within the human copy of the gene. As a further distinction from bLys expressed in stomach, we identified a segment within the 3'UTR of the mRNA which is conserved between the bovine and human blood cell variants of the Lys, but does not have significant sequence homology to any of the bovine lysozyme genes known so far. By sequence comparisons, we present evidence that this segment has been deleted during evolutionary divergence of the stomach Lys. Hence, we describe the sequence of a heretofore unknown bLys, being expressed in granulocytes. Bearings of our observations on the understanding of Lys evolution are discussed, as well as the possibility that the product of this gene may be responsible for the functional Lys activity in bovine milk.

A single point mutation results in A allele-specific exon skipping in the bovine alpha s1-casein mRNA

Bovine alpha s1-casein (alpha s1-CN) allele A is found in low allelic frequencies among different cattle breeds and is known to be characterized by the deletion of amino-acid residues 14 to 26 of the mature protein (as defined via the most common allele B), and a corresponding deletion of 39 bp from its cDNA. Based upon the genomic sequence of bovine alpha s1-CN [Koczan et al., Nucleic Acids Res. 19 (1991) 5591-5596], this allelic deviation can be interpreted as an absence of exon 4 from the A allele mRNA and protein product. We demonstrate that this allelic aberration is not caused by a genomic deletion across the exon-4 DNA, but is correlated with a single point mutation at position +6 in the splice donor sequence distal of exon 4, which results in upstream exon skipping during the serial splice reactions of the A allele alpha s1-CN pre-mRNA. The A-allele-specific mutation at position +6 is able to interrupt the perfect complementarity of the intron-4 splice donor signal (positions one to eight) with U1-snRNA, which may then no longer be able to compensate for a rather weak exon-4 upstream splice acceptor sequence in facilitating the initial binding of U2 auxiliary factor/65-kDa (U2AF65) to that polypyrimidine tract. This interpretation of the exon skipping mechanism in alpha s1-CN allele A is in agreement with similar results obtained [Hoffmann and Grabowski, Genes Dev. 6 (1992) 2554-2568] in an analysis of the rat preprotachykinin-encoding gene and in vitro experiments.

Expression of human lactoferrin in milk of transgenic mice

The expression of human lactoferrin (hLF) in the milk of transgenic mice is described. Regulatory sequences derived from the bovine alpha S1-casein gene were fused to the coding sequence of the hLF cDNA and several lines of transgenic mice were generated. Human LF RNA was detected exclusively in the mammary gland of lactating females and only after the onset of lactation. No aberrant RNA products could be detected using northern blotting and primer extension analysis. The hLF concentrations in the milk ranged from less than 0.1 to 36 micrograms ml-1. Human LF thus expressed did not differ from human milk derived LF, with respect to molecular mass and immunoreactivity with monoclonal and polyclonal antibodies.

Characterization of two novel casein transcripts in rabbit mammary gland

Two clones were isolated from a cDNA library corresponding to mRNAs which accumulate in mid-lactating (14 day) rabbit mammary gland and characterized by DNA sequencing. The two clones sequenced corresponded to two novel casein transcripts (pBRM5 and pBRM42). Relative mRNA abundances for the two clones were assessed by dot-blot analysis. Phylogenetic analysis and comparison of both pBRM5 and pBRM42 with other members of the casein family revealed that the rabbit may be unique among mammals in expressing two alpha s2-casein genes. The presence of two alpha s2-casein genes in the rabbit may be the result of a relatively recent intergenic duplication event.

Organisation of the ovine immunoglobulin C epsilon gene locus: evidence for a deletion 5' of the gene

A cosmid clone containing the ovine and C epsilon and C alpha immunoglobulin heavy chain genes was isolated and characterised. Restriction mapping and sequence analysis showed a high degree of similarity between the bovine and ovine C epsilon loci. Restriction fragment length polymorphism (RFLP) analysis of sheep genomic DNA revealed Mendelian inheritance of polymorphisms with identical variation in allele size for various restriction enzymes. This identical variation suggested that a deletion of approximately 100 bp existed at the 5' end of the smaller alleles.

The secondary structure of milk proteins and their biological function

A brief overview is given of the methods of determining and predicting secondary structure in proteins. The secondary structures of the milk serum proteins, lactoferrin, alpha-lactalbumin, lysozyme, and beta-lactoglobulin, as determined by x-ray crystallography, are compared with the results of a joint prediction method. This comparison evaluates critically the degree of success achieved and helps define what can reasonably be expected from a prediction in the absence of a known structure. The value of supplementary information from spectroscopic methods and the use of templates and sequence information from related proteins in improving the confidence of predictions are illustrated. One point that emerges is the general overprediction of helix content by the joint prediction method such that, for an all-beta protein such as beta-lactoglobulin, the method of Garnier, Osguthorpe, and Robson, applied with the correctly selected decision constants, provides a somewhat better approach. Secondary structure of the caseins can be predicted with less confidence than for globular proteins, and the results should be interpreted as evidence of a propensity to form transient secondary structures of the indicated type in view of the generally open and flexible conformation of caseins in solution.

The ovine Booroola fecundity gene (FecB) is linked to markers from a region of human chromosome 4q

The autosomal Booroola fecundity gene (FecB) mutation in sheep increases ovulation rate and litter size, with associated effects on ovarian physiology and hormone profiles. Analysis of segregation in twelve families (379 female progeny) identified linkage between the mutation, two microsatellite markers (OarAE101 and OarHH55, Zmax > 9.0) and epidermal growth factor (EGF) from human chromosome 4q25 (Zmax > 3.0). The marker OarAE101 was linked to secreted phosphoprotein 1 (SPP1, which maps to chromosome 4q21-23 in man) in the test pedigrees and independent families (Zmax > 9.7). The identification of linkage between the FecB mutation and markers from human chromosome 4q is an important step towards further understanding the control of ovulation rates in mammals.

The isolation and properties of whole casein: some implications for comparative studies

1. Problems in the isolation of whole casein from bovine milk are considered. A summary is given of our experiences in its isolation. 2. The physical characteristics, sedimentation velocity, heterogeneity, absorptivity, nitrogen, phosphorus and carbohydrate contents of whole casein prepared from normal and sub-clinical mastitic milk samples by a variety of methods are compared. The methods are acid precipitation, high-speed centrifugation, with and without added calcium (II), and ammonium sulphate precipitation. 3. A description is given of the low temperature ammonium sulphate procedure preferred for the isolation of whole casein, especially when it is to be used for subsequent fractionation for conformation and micelle studies. 4. The question of the use of bovine casein as a paradigm for the caseins of other mammalian species and the need for further studies of the physical, chemical and biological properties of the caseins are discussed.

Synteny mapping in the bovine: genes from human chromosome 4

Genes homologous to those located on human chromosome 4 (HSA4) were mapped in the bovine to determine regions of syntenic conservation among humans, mice, and cattle. Previous studies have shown that two homologs of genes on HSA4, PGM2 and PEPS, are located in bovine syntenic group U15 (chromosome 6). The homologous mouse genes, Pgm-1 and Pep-7, are on MMU5. Using a panel of bovine x hamster hybrid somatic cells, we have assigned homologs of 11 additional HSA4 loci to their respective bovine syntenic groups. D4S43, D4S10, QDPR, IGJ, ADH2, KIT, and IF were assigned to syntenic group U15. This syntenic arrangement is not conserved in the mouse, where D4s43, D4s10, Qdpr, and Igj are on MMU5 while Adh-2 is on MMU3. IL-2, FGB, FGG, and F11, which also reside on MMU3, were assigned to bovine syntenic group U23. These data suggest that breaks and/or fusions of ancestral chromosomes carrying these genes occurred at different places during the evolution of humans, cattle, and mice.

The multimeric structure and disulfide-bonding pattern of bovine kappa-casein

Bovine kappa-casein was analyzed by SDS/PAGE, MS and amino acid sequence analysis in order to determine its multimeric composition and disulfide-bonding pattern. SDS/PAGE revealed that kappa-casein in the native state can range in size from a monomer to a multimeric structure larger than a decamer. Three types of interchain disulfide linkage, Cys11-Cys11, Cys11-Cys88 and Cys88-Cys88, were all assigned in multimers purified from [14C]carboxymethylated and untreated bulk milk, as well as a milk sample from a kappa-casein-variant-B homozygote Co20. These results indicate that multimerization occurs in a random or at present unpredictable disulfide-bonding pattern regardless of the size of the multimer or the genotype.

Casein, actin, and tubulin expression during early involution in bovine and murine mammary tissue

Hybridization methods and in vitro translation were used to examine the expression and functional condition of messenger RNA encoding caseins and cytoskeletal proteins in the mammary gland during early involution. In the mouse, steady state mRNA levels for alpha-, beta-, and gamma-caseins coordinately decreased to 20% of initial levels between 12 and 72 h after pup removal. In vitro translatability of mouse casein mRNA, as determined by immunoprecipitation, electrophoresis, and gel slice counting, revealed a pattern that closely paralleled mRNA expression. In contrast, bovine casein mRNA levels were only slightly reduced by 72 h postmilking, whereas in vitro translatability decreased by about one-half. Northern blot analysis of total mouse mammary RNA that were hybridized with probes to cytoskeletal proteins showed a gradual decrease of alpha-tubulin mRNA, but an increase in beta-actin mRNA during early involution. Two-dimensional gel analysis of in vitro translated products indicated a concordant increase in beta-gamma-actin. In the cow, beta-actin mRNA at 72 h of involution was equal to or greater than that during lactation. These results demonstrate the generally slower involution response in the cow and suggest that differing regulations are involved. Early events of cellular involution may be related to a reorganization of the cytoskeleton.

Prospects for the genetic engineering of milk

Milk and milk products comprise a substantial fraction of the protein intake of the industrialised West. The establishment of germline manipulation techniques in cows offers opportunities for directly manipulating milk composition to produce products with enhanced nutritional and processing properties. The major milk proteins are encoded by a small number of abundantly expressed single-copy genes and a number of possible manipulations are described. Milk proteins exhibit complex interactions with each other and with other constituents of milk. It will, therefore, be necessary to utilise model systems to evaluate the consequences of these proposed changes before embarking upon the costly and time-consuming process of manipulating the bovine genome.

Localization of two interchain disulfide bridges in dimers of bovine alpha s2-casein. Parallel and antiparallel alignments of the polypeptide chains

Carboxymethylation of bovine skimmed milk with 14C-labelled iodoacetic acid followed by purification of the alpha s2-casein dimer showed that all four cysteine residues in the protein are engaged in disulfide linkages. Mass spectrometry and sequence analysis of cystine-containing tryptic peptides revealed the presence of two interchain disulfide bridges in the protein. Sequence analysis of disulfide-linked peptides resulting from an enzymatic cleavage between the bridges demonstrated that the individual chains in the dimers are either aligned in an antiparallel or a parallel orientation. The identity of some of the disulfide-linked peptides was further verified by performic acid oxidation followed by sequence analysis of the resulting peptides.

Genomic organization of the bovine alpha-S1 casein gene

We report the sequence of the complete bovine alpha-s1 casein gene eludicating for the first time the genomic organization of an alpha-s type casein gene. Extending over 17508 bp the gene is split into 19 exons, ranging in size from 24 bp to 385 bp. Except for the translational stop codon not a single coding triplet of the alpha-s1 reading frame is disrupted by any of the splice junctions, which all confirm to known splice consensus sequences. Nine out of 16 coding exons begin with a 'GAX' codon, specific for glutamate. Splicing of this codon from exon 10 to the preceding exon creates a major phosphorylation site. An intron-exon-intron stretch of 154 bp comprising exons 10 and 13 is found precisely duplicated. Associated with the gene, copies of 8 atriodactyla retroposons are found, 6 of which are interspersed into the sequences of the three longest introns. We discuss the possibility that three functional parts of the gene have been recruited and evolutionary conserved at a time before gene diversification gave rise to the separate evolution of alpha- and beta-type casein-genes.

Bovine lactoferrin mRNA: sequence, analysis, and expression in the mammary gland

The mRNA sequence for bovine lactoferrin expressed in the mammary gland was determined by sequencing three over lapping cDNA clones and by direct sequencing of the mRNA. The mRNA (2351 bases) codes for a 708 amino acid protein with a 19 amino acid signal peptide immediately preceding a sequence identical to the N-terminal 40 amino acids reported for bovine lactoferrin. A putative destabilizing sequence (AUUUA) was identified in the 3'-untranslated region. The nucleic acid sequence and deduced amino acid sequence are highly homologous with other transferrin family members. Lactoferrin mRNA concentrations in bovine mammary tissue were quite low two days before parturition and during lactation but were high three days after the cessation of milking, a sharp contrast from the pattern of regulation of the other milk proteins.

Tertiary and quaternary structural differences between two genetic variants of bovine casein by small-angle X-ray scattering

The casein complexes of bovine milk consist of four major protein fractions, alpha s1, alpha s2, beta, and kappa. Colloidal particles of casein (termed micelles) contain inorganic calcium and phosphate; they are very roughly spherical with an average radius of 650 A. Removal of Ca2+ leads to the formation of smaller protein aggregates (submicelles) with an average radius of 94 A. Two genetic variants, A and B, of the predominant fraction, alpha s1-casein, result in milks with markedly different physical properties, such as solubility and heat stability. To investigate the molecular basis for these differences, small-angle X-ray scattering was performed on the respective colloidal micelles and submicelles. Scattering curves for submicelles of both variants showed multiple Gaussian character; data for the B variant were previously interpreted in terms of two concentric regions of different electron density, i.e., a "compact" core and a relatively "loose" shell. For the submicelle of A, there was a third Gaussian, reflecting a negative contribution due to interparticle interference. Molecular parameters for submicelles of both A and B are in agreement with hydrodynamic data in the literature. Data for the micelles, for which scattering yields cross-sectional information, were fitted by a sum of three Gaussians for both variants; for these, the corresponding two lower radii of gyration represent the two concentric regions of the submicelles, while the third reflects the average packing of submicelles within the micellar cross section. Most of the molecular parameters obtained showed small but consistent differences between A and B, but for submicelles within the micelle several differences were particularly notable: A has a greater molecular weight for the "compact" region of the constituent submicelle (82,000 vs 60,000) and a much greater submicellar packing number (6:1 vs 3:1). Reasons for these and other differences are to be sought in sequence differences and in differences in calcium-binding sites and charge distribution.

Genomic analysis of the major bovine milk protein genes

The genomic arrangement of the major bovine milk protein genes has been determined using a combination of physical mapping techniques. The major milk proteins consist of the four caseins, alpha s1 (CASAS1), alpha s2 (CASAS2), beta (CASB), and kappa (CASK), as well as the two major whey proteins, alpha-lactalbumin (LALBA) and beta-lactoglobulin (LGB). A panel of bovine X hamster hybrid somatic cells analyzed for the presence or absence of bovine specific restriction fragments revealed the genes coding for the major milk proteins to reside on three chromosomes. The four caseins were assigned to syntenic group U15 and localized to bovine chromosome 6 at q31-33 by in situ hybridization. LALBA segregated with syntenic group U3, while LGB segregated with U16. Pulsed-field gel electrophoresis confirmed genetic mapping results indicating tight linkage of the casein genes. The four genes reside on less than 200 kb of DNA in the order CASAS1-CASB-CASAS2-CASK. Multiple restriction fragment length polymorphisms were also found at the six loci in three breeds of cattle.

High-performance liquid chromatography of casein hydrolysates phosphorylated and dephosphorylated. I. Peptide mapping

A mixture of small peptides of molecular weight averaging 1000 daltons, obtained by controlled hydrolysis of casein with proteases, chymotrypsin and trypsin, was separated by size-exclusion and reversed-phase high-performance liquid chromatography. Peptides were identified and located in the known casein structures from their amino acid content and their N- and C-terminal amino acid analyses. The primary structure of peptides identified from casein hydrolysate phosphorylated and casein hydrolysate dephosphorylated is presented.

Isolation of monoclonal antibodies monospecific for bovine kappa-casein

Bovine kappa-casein represents a major portion of the total protein present in milk and is required for formation of the caseinate micelles responsible for the transportation of both calcium and phosphorous. Two monoclonal antibodies directed against bovine kappa-casein have been isolated. Both monoclonal antibodies are highly specific for bovine kappa-casein. Western analysis of denatured kappa-casein suggests epitope specificity is, in part, conformationally dependent. Additional epitope mapping with chymosin and neuraminidase also suggest antibody binding is in the region of the amino acid sequence Pro-Thr-Thr at positions 92 to 94 and 134 to 136.

Restriction fragment length polymorphism analysis of the kappa-casein locus in cattle

The two common genetic variants (A and B) of bovine kappa-casein originate from two point mutations in the codons for the aminoacids in position 136 and 148. These mutations give rise to polymorphic sites for the restriction endonucleases Hin dIII, AluI, HinfI, Mbo II and TaqI. We have examined DNAs of several Italian Friesian cows and bulls of known and unknown genotype by Southern analyses using kappa-casein cDNA probes. Restriction fragment length polymorphisms (RFLPs) specific for the A and B alleles were identified for each of the above enzymes, except for AluI, which has a non-polymorphic site 12bp away from the polymorphic one. We have also found two new polymorphic sites for MboII and TaqI in the non-coding regions. These sites differentiate the A allele into two new variants, named A1 and A2. The RFLP analysis permits the characterization of kappa-casein alleles even in the absence of their expression. This should facilitate selective breeding programmes aimed at increasing the frequency of the kappa-casein B allele whose product improves the cheesemaking properties of milk.

Cloning and sequencing of a complementary deoxyribonucleic acid coding for a bovine alpha s1-casein A from mammary tissue of a homozygous B variant cow

A cDNA clone for bovine alpha s1-casein variant A was isolated from a mammary gland cDNA library using a synthetic degenerate oligonucleotide probe. The largest Pst I insert containing an EcoR I site was sequenced. It contained 1090 base pairs, 47 in the 5' noncoding region, 603 in the coding region and 440 in the 3' noncoding region. The nucleotide sequence was compared with three published cDNA sequences for alpha s1-casein variant B. The most obvious difference was the absence of the 39 bases encoding the 13 amino acids that are present in the B variant but absent from the A variant. In addition, five other single base positions differed within individual codons among the four sequences at the third base for each codon, but this did not change the amino acids encoded. There were, however, a number of differences found in the 3' noncoding region. The isolated cDNA was subjected to site-directed mutagenesis to replace a Val-Ile dipeptide with Phe-Phe to increase the chymosin sensitivity of the protein. When the milk proteins from mammary gland tissue extracts were typed, the alpha s1-casein A gene product was not detected.

Caseins of various origins and biologically active casein peptides and oligosaccharides: structural and physiological aspects

The first part of the present review is focused on structural aspects concerning the so far studied casein fractions of various origins: they are compared to the four classical major bovine caseins (alpha s1-, alpha s2-, beta- and kappa). The calcium-sensitive casein fractions are always phosphorylated whereas kappa-caseins are glycosylated. The study of the casein genes showed that the calcium-sensitive caseins diverged from a common ancestral gene and during the evolution, intergenic and intragenic duplications occurred. The considerable conservation of the phosphorylation sites emphasizes the importance of phosphorylated residues for the function of caseins, i.e. the formation of micelles and the binding of Ca2+. In kappa-caseins all the prosthetic sugar groups are linked by O-glycosidic linkages: their number varies from 0 to 5 in bovine kappa-casein and up to 10 in human kappa-casein. The structures of the known kappa-casein carbohydrate moieties are described. Finally the milk clotting process (interaction kappa-casein/chymosin) is compared to the blood clotting process (interaction fibrinogen/thrombin): a large number of similarities could be noted between both clotting phenomena. The second part of the review is devoted to the study of short casein peptides endowed with various biological activities. Some of them behaved as immunomodulators or casomorphins or angiotensin I converting enzyme inhibitors; others demonstrated an effect on platelet functions. A 'strategic zone' containing immunostimulating and opioid peptides could be located in cow and human beta-caseins. Furthermore bitter peptides, emulsifying peptides, calcium absorption enhancing peptides, chymosin-inhibiting peptides, have also been described and several further properties have been attributed to the kappa-caseinoglycopeptide; two tetrasaccharides isolated from the latter possess blood group activities. In conclusion caseins, the main milk proteins, should not only be considered as a nutriment but as a possible source of biologically active components. If, in the future, some of the discussed active peptides cannot be characterized in vivo, they can all, nevertheless, be synthesized and used either as food additives or in pharmacology.

Isolation and characterization of the bovine kappa-casein gene

1. The bovine kappa-casein gene has been isolated as a series of overlapping lambda 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 kappa-casein gene, together with its upstream sequence, confirms previous conclusions that it is unrelated to the calcium-sensitive-casein gene family to which it is linked. Evidence is presented which supports a previous suggestion that kappa-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 kappa-casein gene, compared with the repeat elements and exons, are A + T-rich. 5. Among the lambda 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.

Casein gene expression in bovine mammary gland

The objectives were to examine the rate of synthesis of casein mRNA transcripts in bovine mammary tissue at different hormonal states and to study the effects of hormonal stimuli (insulin, hydrocortisone, and prolactin) on the accumulation of casein mRNA and on the rate of protein secretion by epithelial cells from bovine mammary tissues. Total cytoplasmic RNA was extracted from mammary tissues of cows obtained by biopsy (8 mo pregnant) and upon slaughter (lactating). The relative specific activities of cytoplasmic mRNA for alpha s1-, alpha s2-, beta-, and kappa-casein were about 3.2, 4.6, 3.3, and 4.5-fold higher in tissues of lactating cows than in those of 8 mo pregnant cows. Mammary alveolar epithelial cells retained hormone-inducible milk protein gene expression for total milk protein gene expression for total milk protein secretion and for alpha s1- and beta-casein messages. Prolactin, even in the absence of insulin and hydrocortisone, induced significant amounts of milk protein mRNA. Hydrocortisone in the presence of prolactin amplified the lactogenic effects on mammary epithelium. Maximal induction of beta-casein mRNA and protein secretion occurred when all three hormones were present.

Calcium-induced associations of the caseins: a thermodynamic linkage approach to precipitation and resolubilization

Calcium-induced changes in protein solubility play a role in a variety of important biological processes including the deposition of bone and dentin and the secretion of milk. The phenomena of salt-induced (calcium) precipitation of proteins (salting-out), and the resolubilization of these proteins at higher salt concentrations (salting-in) have been studied and quantitated using an approach based on the concepts of Wyman's thermodynamic linkage. Salting-out has been described by a salt-binding constant, k1, the number of moles of salt bound per mole of protein, n, and S1, the fraction soluble at saturation of n; salting-in has been described by corresponding constants k2, m, and S2. Analysis of salt-induced solubility profiles was performed using nonlinear regression analysis. Results of calcium-induced solubility profiles of two genetic variants of alpha s1-casein (alpha s1-A), (alpha s1-B), and beta-casein C (beta-C) at 37 degrees C, where hydrophobic interactions are maximized, showed no salting-in behavior and for salting-out, yielded k1 values of 157, 186, and 156 liters.mol-1 and n values of 8, 8, and 4, respectively. The values of k1 can be correlated with the apparent association constant for calcium binding to casein, while the values of n can be correlated with the number of calcium binding sites of the respective caseins. At 1 degree C, where hydrophobic interactions are minimized, nominally only hydrophilic and electrostatic interactions can be linked to the salt-induced solubility profiles; here beta-C is totally soluble at all calcium concentrations and alpha s1-B and alpha s1-A were now found to have salting-in parameters, k2 and m, of 2.5 liters.mol-1 and 4, and 11 liters.mol-1 and 8, respectively. alpha s1-A is more readily salted-in and studies on the variation of S1 with added KCl for this protein at 1 degree C indicated that salting-in is also mainly electrostatic in nature and may result from competition between K+ and Ca2+ for binding sites rather than from solute-solvent interactions as previously proposed. Comparison of k1 and k2 values between the two genetic variants, coupled with the known sequence differences (the A variant is a linear deletion of 13 amino acids) suggest the existence of a hydrophobically stabilized ion pair in alpha s1-B which is deleted in alpha s1-A; it is speculated that such bonds may play a role in other calcium-induced changes in protein solubility.

Isolation and characterization of the Bos taurus beta-casein gene

The expression of casein genes in the mammary cells is regulated by peptide and steroid hormones. To investigate the controlling mechanisms we have isolated and characterized the bovine beta-casein gene. The gene has the size of 8.6 kb, which is 7.8 times longer than the corresponding mRNA composed of nine exons. The genomic clones include additional 8.5-kb and 4.5-kb sequences of the 5'- and 3'-flanking regions. We have determined the sequences of the 5' and 3' ends of the gene and compared them with the respective sequences of the rat beta-casein gene. Conserved sequences are identical or homologous to the potential binding sites for nuclear factors and for glucocorticoid and progesterone receptors. The regulatory region contains two different TATA signals and a repeat sequence between them.

Molecular cloning and expression of bovine kappa-casein in Escherichia coli

A cDNA library was constructed using poly(A) +RNA from bovine mammary gland. This cDNA library of 6000 clones was screened employing colony hybridization using 32P-labelled oligonucleotide probes and restriction endonuclease mapping. The cDNA from the selected plasmid, pKR76, was sequenced using the dideoxy-chain termination method. The cDNA insert of pKR76 carries the full-length sequence, which codes for mature kappa-casein protein. The amino acid sequence deduced from the cDNA sequence fits the published amino acid sequence with three exceptions; the reported pyroglutamic acid at position 1, tyrosine at position 35, and aspartic acid at position 81 are, respectively, a glutamine, a histidine, and an asparagine in the clone containing pKR76. The MspI-, NlaIV-cleaved fragment (630 base pair) from the kappa-casein cDNA insert has been subcloned into expression vectors pUC18 and pKK233-2, which contain a lac promoter and a trc promoter, respectively. Escherichia coli cells carrying the recombinant expression plasmids were shown to produce kappa-casein protein having the expected mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and being recognized by specific antibodies raised against natural bovine kappa-casein.

Cloning and sequence analysis of bovine beta-casein cDNA

A bovine beta-casein cDNA clone was isolated from a cDNA library prepared from mammary gland mRNA. Sequence analysis revealed 25 nucleotides (nt) of the 5' noncoding region, 672 nt of the complete sequence coding and a 3' region of approximately 500 nt. When the nucleotide sequence of bovine beta-casein cDNA is compared to rat beta-casein cDNA (5), a high degree of homology is observed in the first 100 nt corresponding to the signal peptide of the pre-beta-caseins.

Cloning and nucleotide sequence of the bovine beta-lactoglobulin gene

A clone coding for beta-lactoglobulin A has been isolated from a cDNA bank constructed from poly(A+)mRNA isolated from the bovine mammary gland. Its nucleotide sequence codes for the beta-lactoglobulin A, from amino acid residues Leu-11 to Ile-162, as based on the amino acid sequence reported by Braunitzer et al. [Z. Physiol. Chem. 354 (1973) 867-878]. In addition to the 455-bp coding sequence, our clone pB beta L4-10 contains a 3'-nontranslated region of approx. 270 bp.

Some guidelines for identification of recognition sequences: regulatory sequences frequently contain (T)GTG/CAC(A), TGA/TCA and (T)CTC/GAG(A)

Inspection of many proposed recognition signal sequences shows that TGTG/CACA, GAGA/TCTC or their triplet subsets, and TGA/TCA occur frequently. These repeated elements, conserved in recognition sequences from evolutionarily distant organisms, are likely to possess unique structural characteristics. Recurrence of these oligomers may aid in identification of further regulatory sequences in upstream or other regions. Another class of recognition sequences is GC-rich. At present there are only a few examples of this class. It is likely that these sequences function via a different mechanism.

Evolution of the casein multigene family: conserved sequences in the 5' flanking and exon regions

The rat alpha- and bovine alpha s1-casein genes have been isolated and their 5' sequences determined. The rat alpha-, beta-, gamma- and bovine alpha s1-casein genes contain similar 5' exon arrangements in which the 5' noncoding, signal peptide and casein kinase phosphorylation sequences are each encoded by separate exons. These findings support the hypothesis that during evolution, the family of casein genes arose by a process involving exon recruitment followed by intragenic and intergenic duplication of a primordial gene. Several highly conserved regions in the first 200 base pairs of the 5' flanking DNA have been identified. Additional sequence homology extending up to 550 base pairs upstream of the CAP site has been found between the rat alpha- and bovine alpha s1-casein sequences. Unexpectedly, the 5' flanking promoter regions are conserved to a greater extent than both the entire mature coding and intron regions of these genes. These conserved 5' flanking sequences may contain potential cis regulatory elements which are responsible for the coordinate expression of the functionally-related casein genes during mammary gland development.

Spontaneous reiterations of DNA sequences near the ends of adenovirus type 3 genomes

Repeated passage of adenovirus type 3 in HeLa cells has led to a novel stock of variant genomes. Most of the DNA molecules in this stock are characterized by deletions and substitutions of DNA sequences near the left end of the adenovirus type 3 genome map, as reported earlier (C.C. Robinson and C. Tibbetts (1984) Virology 137, 276-286). In this report the characterization of the variant genomes is extended and reveals elongated DNA molecules bearing tandem repetitions of viral DNA sequences near the left and right ends of the viral DNA. Evidence is also presented supporting the cellular DNA origin of short insert sequences found in substitution variants. The elongated variants are of interest because of their novel repeated DNA structures. The locations of these aberrant sequences raise questions about their potential impact on viral gene expression.

Complete sequence of ovine alpha s2-casein messenger RNA

The primary structure of mRNA coding for ovine alpha s2 casein has been determined by chemical sequencing of three cDNA clones and the primer extension products of the longest one. The mRNA was 1,024 nucleotides long, excluding the poly(A) tail. The length of the 5' noncoding, coding and 3' noncoding regions was 53, 669 and 302 nucleotides, respectively. A comparison of the nucleotide sequence of ovine alpha s2-casein and guinea-pig casein A mRNAs revealed an extensive homology in the 5' and 3' noncoding regions. The deduced amino acid sequence of ovine alpha s2-casein was compared with its bovine and guinea-pig counterparts. Moreover, an heterogeneity was evidenced in the mRNA population of the alpha s2-casein.

Construction and identification of recombinant plasmids carrying cDNAs coding for ovine alpha S1-, alpha S2-, beta-, kappa-casein and beta-lactoglobulin. Nucleotide sequence of alpha S1-casein cDNA

An ovine mammary cDNA library has been constructed from total poly(A)+ RNA isolated from the mammary gland of a lactating ewe, using a classical procedure. Blunt-ended double-stranded cDNAs prepared with reverse transcriptase and nuclease S1 were tailed with dCTP, inserted into the dGMP-tailed PstI site of plasmid pBR322 and cloned in E. coli. Five series of homologous clones representing abundant messenger RNAs (strong hybridization with a single-stranded cDNA probe generated from total poly(A)+ RNA) were selected using each time a different predominant cloned ds-cDNA as probe, then identified by positive hybridization-translation of the cognate mRNA and subsequent immunoprecipitation and electrophoresis of the protein. The lengths of alpha s1-, alpha s2-, beta-, kappa-casein and beta-lactoglobulin mRNAs are in the range of 1.2, 1.1, 1.25, 1.0 and 0.85 kb, respectively, as determined by Northern blotting analysis. Five homologous mRNAs of similar sizes were identified in the porcine species by dot blot hybridization and Northern analyses. The nucleotide sequence of alpha s1-casein mRNA was determined by sequencing, according to Maxam and Gilbert, both a 1080 bp long cloned ds-cDNA and a ss-cDNA (268 nucleotides) generated by 5' extension of a 5' terminal truncated radiolabeled fragment (83 bp) of the relevant ds-cDNA, used as primer for reverse transcription. The 3' non coding region (431 nucleotides, excluding the poly(A) tail) represents 70% of the length of the coding region (618 nucleotides) flanked by a 61 nucleotide 5' region. Comparison of sequences of ovine and bovine, rat and guinea-pig alpha s1-casein mRNAs has revealed a greater homology in the 3' and especially 5' non coding regions. In the reading frame, the conserved regions are essentially those corresponding to the signal peptide and phosphopeptide domains. The derived 206 amino acid sequence of ovine pre-alpha s1-casein differs from that of its bovine counterpart (genetic variant B) by 24 amino acid substitutions and a deletion of 8 amino acid residues occurring in the polypeptide chain of the mature protein. Such a variation (84% homology only) in two phylogenetically closely related species indicates a high rate of evolution of alpha s1-casein.