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

Quantification of the kokumi peptide, γ-glutamyl-valyl-glycine, in cheese: Comparison between cheese made from cow and ewe milk

Recent studies have shown that several types of cheese contain kokumi γ-glutamyl dipeptides, and the kokumi tripeptide, γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly), is a component of various fermented foods. The quantification of γ-Glu-Val-Gly in various types of cheese was herein conducted by HPLC-tandem mass spectrometry followed by derivatization with 6-aminoquinoyl-N-hydroxysuccinimidyl-carbamate. The γ-Glu-Val-Gly concentrations were between 0.35 and 0.59 μg/g in cheese made from ewe milk, but were not detected in cheese made from cow milk. The amino acid sequences of major milk proteins showed that the β-caseins of sheep had the Val-Gly sequence at the 9-10 position, whereas β-caseins of cows contained a Pro-Gly sequence at the same position. The Val-Gly sequence was absent in other caseins of sheep and cattle. These results suggest that the different γ-Glu-Val-Gly concentrations present in cheese made from cow and ewe milk are due to differences in the amino acid sequences of caseins.

DNA methylation and transcription in a distal region upstream from the bovine AlphaS1 casein gene after once or twice daily milking

Once daily milking (ODM) induces a reduction in milk production when compared to twice daily milking (TDM). Unilateral ODM of one udder half and TDM of the other half, enables the study of underlying mechanisms independently of inter-individual variability (same genetic background) and of environmental factors. Our results show that in first-calf heifers three CpG, located 10 kb upstream from the CSN1S1 gene were methylated to 33, 34 and 28%, respectively, after TDM but these levels were higher after ODM, 38, 38 and 33%, respectively. These methylation levels were much lower than those observed in the mammary gland during pregnancy (57, 59 and 50%, respectively) or in the liver (74, 78 and 61%, respectively). The methylation level of a fourth CpG (CpG4), located close by (29% during TDM) was not altered after ODM. CpG4 methylation reached 39.7% and 59.5%, during pregnancy or in the liver, respectively. CpG4 is located within a weak STAT5 binding element, arranged in tandem with a second high affinity STAT5 element. STAT5 binding is only marginally modulated by CpG4 methylation, but it may be altered by the methylation levels of the three other CpG nearby. Our results therefore shed light on mechanisms that help to explain how milk production is almost, but not fully, restored when TDM is resumed (15.1±0.2 kg/day instead of 16.2±0.2 kg/day, p<0.01). The STAT5 elements are 100 bp away from a region transcribed in the antisense orientation, in the mammary gland during lactation, but not during pregnancy or in other reproductive organs (ovary or testes). We now need to clarify whether the transcription of this novel RNA is a consequence of STAT5 interacting with the CSN1S1 distal region, or whether it plays a role in the chromatin structure of this region.

Molecular characterization and phylogenetic analysis of a yak (Bos grunniens) κ-casein cDNA from lactating mammary gland

κ-Casein is one of the major proteins in the milk of mammals. It plays an important role in determining the size and specific function of milk micelles. We have previously identified and characterized a genetic variant of yak κ-casein by evaluating genomic DNA. Here, we isolate and characterize a yak κ-casein cDNA harboring the full-length open reading frame (ORF) from lactating mammary gland. Total RNA was extracted from mammary tissue of lactating female yak, and the κ-casein cDNA were synthesized by RT-PCR technique, then cloned and sequenced. The obtained cDNA of 660-bp contained an ORF sufficient to encode the entire amino acid sequence of κ-casein precursor protein consisting of 190 amino acids with a signal peptide of 21 amino acids. Yak κ-casein has a predicted molecular mass of 19,006.588 Da with a calculated isoelectric point of 7.245. Compared with the corresponding sequences in GenBank of cattle, buffalo, sheep, goat, Arabian camel, horse, and rabbit, yak κ-casein sequence had identity of 64.76-98.78% in cDNA, and identity of 44.79-98.42% and similarity of 53.65-98.42% in deduced amino acids, revealing a high homology with the other livestock species. Based on κ-casein cDNA sequences, the phylogenetic analysis indicated that yak κ-casein had a close relationship with that of cattle. This work might be useful in the genetic engineering researches for yak κ-casein.

DNA polymorphism at the casein loci in sheep

By using seven endonucleases and four bovine cDNA probes specific for alpha S1-, alpha S2-, beta-, and kappa-casein genes, nine restriction fragment length polymorphisms (RFLPs) have been found in the sheep orthologous DNA regions. In contrast to the low level of variation observed at the protein level, these DNA polymorphisms determine a high level of heterozygosity and, therefore, represent useful tools for genetic analyses since they can also be obtained without the need for gene expression. In fact, informative matings suggest that in sheep, as in cattle, the four loci are linked.

Genotyping of bovine kappa-casein (kappa-CNA, kappa-CNB, kappa-CNC, kappa-CNE) following DNA sequence amplification and direct sequencing of kappa-CNE PCR product

Genomic DNA isolated from blood and semen of dairy cattle with known kappa-casein (kappa-CN) genotypes was subjected to Southern blot hybridization and polymerase chain reaction (PCR) using up to 14 restriction endonucleases. kappa-casein genotypes AA, AB and BB were identified using Hin dIII and Hin fI while genotypes with kappa-CNC and kappa-CNE were misidentified. Direct sequencing of the PCR product (kappa-CN EE) showed a substitution of guanine (kappa-CNA,B) by adenine (kappa-CNE) which creates a HaeIII restriction site. Therefore using PCR followed by Hin dIII or HinfI and Hae III digest allows discrimination between kappa-casein A, B and E directly at the DNA level.

The bovine gene map

The present status of the bovine gene map as well as some of the methods and strategies important for future efforts in completing the gene map of cattle are reviewed.

Detection of bovine αs1-casein genomic variants using the allele-specific polymerase chain reaction

A method was developed to distinguish between genotypic variants B and C of bovine alpha s1-casein, using the allele-specific polymerase chain reaction (ASPCR). The alpha s1-casein genotype determined for 17 Jersey cows by the ASPCR method was confirmed by typing the alpha s1-casein milk proteins on isoelectric focusing gels. Using the ASPCR method described, rapid analysis of the alpha s1-casein genotype of bulls is now possible. In addition, kappa-casein genotypes can be determined from the same PCR reaction.

The sequence of porcine alpha s1-casein cDNA: evidence for protein variants generated by altered RNA splicing

A cDNA library was constructed from mRNA isolated from lactating porcine mammary gland and screened with a bovine alpha s1-casein cDNA clone. Three classes of cDNA isolated varied in the number of bases within the coding region. The full length porcine alpha s1-casein cDNA is 1124bp and codes a preprotein of 206 amino acids. The other two classes of alpha s1-casein cDNA lacked 18bp and 60bp respectively when compared to the 1124-bp cDNA sequence. PCR amplification confirmed the presence of these sequences in total RNA. These differences appear to be due to altered RNA splicing.

Cloning and sequencing of the porcine kappa-casein cDNA

cDNA clones encoding porcine kappa-casein were isolated and sequenced. The porcine kappa-casein cDNA is 851 bp in length and encodes a preprotein of 188 amino acids.

Analysis of polymorphism in the bovine casein genes by use of the polymerase chain reaction

Methods have been devised for detecting polymorphisms in the bovine beta- and kappa-casein genes using the polymerase chain reaction (PCR) followed either by restriction enzyme digestion (to reveal a restriction fragment length polymorphism (RFLP] or by hybridization of an allele-specific oligonucleotide. These methods, as well as being faster and more sensitive than traditional RFLP methods, are of more general applicability since they can detect any change in DNA sequence. They require only a small sample of blood or semen and are applicable to animals of any age or sex. These methods make possible large-scale screening and thus selection for alleles at these loci. Typing of blood DNA can give erroneous results when the animal concerned is a twin; however, this can be overcome by retesting using milk or semen. Analysis of the kappa-casein genotype of Holstein-Friesian bulls gives frequencies for the A and B alleles of 0.80 and 0.20 respectively. Selection in favour of the B allele, which is superior for cheese production, could thus have a large effect. The A3 and B alleles at the beta-casein locus have been shown to be rare in the Holstein-Friesian population. Linkage disequilibrium exists between beta-casein B and kappa-casein B.

A method for kappa-casein genotyping of bulls

A method for kappa-casein genotyping in bulls has been developed. By analysis of DNA polymorphisms we are able to discriminate between the kappa-casein variant A and B in the bulls. This method will be an efficient tool in selection for the most desirable kappa-casein variant.

Identification of bovine kappa-casein genotypes at the DNA level

By using a bovine kappa-Cn cDNA as probe and the PstI endonuclease we demonstrate that the DNA restriction patterns of kappa-Cn AA and kappa-Cn BB cows are different. Besides two invariant fragments (about 6.8kb and 1.1kb) the former shows two fragments of about 4.3 kb and 0.3 kb and the latter one fragment of about 4.6 kb. kappa-Cn AB cows show intermediate pattern. Therefore, it is possible to determine the bovine kappa-Cn genotypes even in absence of gene product.

[Genetic polymorphism of k-casein gene exon 4 and its cor-relation with milk production traits in Chinese Holsteincows.]

K-casein gene was regarded as a candidate gene for milk production traits of cows. In this study, a 779 bp fragment of k-casein gene of Chinese Holstein was amplified by polymerase chain reaction (PCR), the polymorphisms of three loci of k-casein gene were detected by PCR-RFLP with restriction endonuclease Taq, Hind, Pst. After sequencing, T/C single nucleotide polymorphism (SNP) was identified at nucleotide 10 891C/A SNP was identified at nucleotide 10 927 and G/A SNP was identified at nucleotide 10 988 in exon4 of k-casein gene. Both alleles (A and B) of three loci were found in the population that showed low polymorphism. The gene frequencies of A and B were 86.03% and 13.97%, respectively. The genotype frequencies of AA, AB, and BB were 73.71%, 24.63%, and 1.66%, respectively. Statistical results of c2 test indicated that three polymorphism sites in the population fitted with Hardy-Weinberg equilibrium (P > 0.05). Meanwhile, the effect of polymorphism of k-casein gene on milk production traits was analyzed. The results indicated that in the three loci, the different genotype of k-casein gene had no significant influence on milk yield and milk protein percent (P > 0.05). The cows with genotypes BB and AB showed higher milk fat percent than those with genotype AA ( P < 0.05 ) ; with genotype AB showed higher fat protein ratio than those with genotype AA ( P < 0.05 ). The polymorphism of the three loci in the experimental population is closely linked. The conclusion is that k-casein B allele can be used as the molecular genetic markers of modifying milk fat percent in Chinese Holstein cows.

Characterization of New Milk-derived Inhibitors of Angiotensin Converting EnzymeIn VitroandIn Vivo

Inhibition of angiotensin converting enzyme (ACE) has been observed with a variety of different peptides, and peptide fragments with inhibitory capabilities have been identified within many different proteins, including milk proteins. The purpose of this study therefore was to identify new short peptides with inhibitory properties from the primary structure of milk proteins and to characterize them in vitro and in vivo, since no milk derived ACE inhibitors have previously been evaluated for their ability to inhibit ACE in vivo. In vitro, 8 of 9 dipeptides were found to be competitive inhibitors of ACE. The IC50 was significantly lower when an angiotensin I-like substrate was used, than when a bradykinin-like substrate was used. Using three different in vivo models for ACE inhibition, a very moderate effect was observed for three of the new peptides, but only for up to 6 or 12 minutes. Nothing was observed with two reference compounds that are reported to be hypotensive ACE-inhibitors derived from milk proteins. This raises the question whether the mechanism of hypotensive action is straightforward inhibition of ACE in vivo.

Nomenclature of the Proteins of Cows’ Milk—Sixth Revision

This report of the American Dairy Science Association Committee on the Nomenclature, Classification, and Methodology of Milk Proteins reviews changes in the nomenclature of milk proteins necessitated by recent advances of our knowledge of milk proteins. Identification of major caseins and whey proteins continues to be based upon their primary structures. Nomenclature of the immunoglobulins consistent with new international standards has been developed, and all bovine immunoglobulins have been characterized at the molecular level. Other significant findings related to nomenclature and protein methodology are elucidation of several new genetic variants of the major milk proteins, establishment by sequencing techniques and sequence alignment of the bovine caseins and whey proteins as the reference point for the nomenclature of all homologous milk proteins, completion of crystallographic studies for major whey proteins, and advances in the study of lactoferrin, allowing it to be added to the list of fully characterized milk proteins.

Multispecies comparison of the casein gene loci and evolution of casein gene family

Caseins, the major milk proteins, are present in a genomic cluster spanning 250-350 kb. The divergence at the coding level between human, rodent, and cattle sequences is rather extensive for most of the genes in this region. Nevertheless, comparative analysis of genomic sequences harboring the casein gene cluster region of these species (with equal evolutionary distances 79-88 Myr) shows that the organization and orientation of the genes is highly conserved. The conserved gene structure indicates that the molecular diversity of the casein genes is achieved through variable use of exons in different species and high evolutionary divergence. Comparative analysis also revealed the presence within two species of uncharacterized casein family members and ruled out the previously held notion that another gene family, located in this region, is primate-specific. Several other new genes as well as conserved noncoding sequences with potential regulatory functions were identified. All genes identified in this region are, or are predicted to be, secreted proteins involved in mineral homeostasis, nutrition, and/or host defense, and are mostly expressed in the mammary and/or salivary glands. These observations suggest a possible common ancestry for the genes in this region.

A short note on DNA lactotypes in the Churra and Manchega sheep breeds

The structure and genetic diversity of the Spanish dairy breeds, Churra and Manchega, is analyzed by means of DNA lactotypes observed in alpha(s1)-, alpha(s2)-, beta- and kappa-ovine caseins. The inter-racial distribution of the casein genotypes is also analyzed. The two breeds differ quantitatively as well as qualitatively in their lactotypes. The proportions of unique lactotypes in Churra and Manchega reveal a high degree of within breed diversity. Breed genetic diversity is greater in Manchega (1.28) than Churra (1.53). The probability combination test indicates the existence of significant inter-racial differences.

Molecular genetics as a diagnostic tool in farm animals

In this review, the importance of molecular genetics for diagnostic applications in animal production and breeding is underlined. Recently, several new techniques and methods based on gene technology have been developed, such as the polymerase chain reaction, fluorescence in situ hybridization, and the use of microsatellite polymorphism. The examples include detection of favourable alleles of genes coding for milk proteins, recognition of negative recessive alleles in hereditary syndromes, the use of microsatellite variants for breeding purposes and parentage control, and application of specific DNA-probes for identification of Y-chromosome-bearing spermatozoa and the sex of embryos. It is to be understood that this list is not complete and more applications will undoubtedly show up in the future. For this review, the authors have mainly selected areas where they themselves or their co-workers have gained experience.

Characterization of the CSN1AG allele of the bovine alpha s1-casein locus by the insertion of a relict of a long interspersed element

The bovine CSN1AG allele is associated with a lower proportion of alpha s1-casein in milk and is characterized by an insertion in the last noncoding exon (19th). According to DNA sequence analysis, the location, length, and origin of the insertion characterizing the bovine CSN1AG allele have been identified. This insertion interrupts the 19th exon between nucleotides 58 and 59, is 371 bp long, and has a high level of homology with relicts of long interspersed elements of retropositional origin. Northern blot analysis shows that the inserted element is transcribed and that the number of transcripts of the CSN1AG allele is less than one-half of the number of transcripts of the CSN1AB allele. The lower amount of alpha s1-casein in milk obtained from cows carrying the CSN1AG allele can be explained by a reduced mRNA stability. Furthermore, a method has been developed using polymerase chain reaction for identification of the carriers of the CSN1AG allele.

High-level expression of bovine alpha s1-casein in milk of transgenic mice

The bovine alpha s1-casein gene, isolated from a cosmid library, was introduced into the murine germline. Transgene expression occurred in all transgenic mice, and was confined to the lactating mammary gland. Half of the mouse lines (five out of ten) expressed at relatively high expression levels (> 1 mg ml-1). The highest levels of expression were obtained with a transgene containing 14.2 kb of 5' flanking sequence, in two cases expression levels comparable to (10 mg ml-1) or well above (20 mg ml-1) alpha s1-casein levels in bovine milk were obtained. Transcription initiation occurred at the same site in the bovine alpha s1-casein gene in transgenic mouse as in the cow. A marked induction of expression occurred at parturition rather than at mid-pregnancy, and thus resembled the bovine rather than the murine developmental expression pattern. Bovine alpha s1-casein specific immunoblotting and RIA were developed for characterization and quantification of the recombinant protein. Using these assays, the properties of the recombinant protein could not be distinguished from those of the natural bovine protein. In spite of the high-level tissue-specific and correctly regulated developmental expression of the transgene, expression levels were integration-site dependent. This may indicate that not all cis-acting regulatory elements involved in bovine alpha s1-casein expression were included in the transgene.

Computer analysis of distribution of putative cis- and trans-regulatory elements in milk protein gene promoters

Multiple alignment of 28 milk protein gene promoters belonging to seven protein superfamilies is described. In these gene promoters three groups of common motifs were found: group I--specific for all milk protein gene promoters; group II--specific only for one gene superfamily; and group III--motifs shared by several gene superfamilies. Motifs of group I and III do not have any preferential location in the promoters, while group II motifs are located in the proximal part, from -36 to -224. Milk protein gene promoters were analysed for presence of putative binding sites for nine transcription factors important for the expression of this group of genes. The transcription factor binding sites for C/EBP, CTF/NF1, MAF and MGF were found in all promoters investigated. The set of putative transcription factor binding sites or response elements for GRE, IRE, PMF, STR and YY1 is unique for every gene superfamily.

Mammary Stat5 abundance and activity are not altered with lactation state in cows

Stat5 is a key intracellular mediator of prolactin signalling and can activate transcription of milk proteins in response to prolactin. Therefore, in animals such as mice where lactation is dependent on prolactin, Stat5 is likely to play an important role in establishing or maintaining lactation in the mammary gland. However, little is known about its role in lactation in the dairy cow. In order to address this, the levels of Stat5a and Stat5b protein, mRNA and Stat5 DNA-binding activity were measured in mammary tissue from mice and cows at different lactational states. In the cow, Stat5a and Stat5b protein and mRNA levels, as well as Stat5 DNA-binding activity were unaltered between pregnancy and established lactation. In contrast, in the mouse Stat5a and Stat5b protein, as well as Stat5 DNA-binding activity were clearly increased during lactation whereas Stat5a and Stat5b mRNA levels were highest during pregnancy as has been previously described. In both species only a minority of the epithelial cell nuclei were Stat5 positive during established lactation. These results suggest that there are significant differences in the biological role of Stat5 in controlling lactation between ruminants and rodents.

Kappa-casein alleles in Zebu and cross-bred (1/2 Friesian, 1/4 Jersey, 1/4 Hariana) cattle from India using polymerase chain reaction and sequence-specific oligonucleotide probes (PCR-SSOP)

Primers and probes were designed to identify two common alleles CASK-A and CASK-B. A local breed of cross-bred cattle produced to improve the quality and quantity of milk, were studied for the alleles of kappa-casein (kappa-casein) gene using polymerase chain reaction and hybridization with sequence specific oligonucleotide probes (PCR-SSPO).

Characterization of phosphate sites in native ovine, caprine, and bovine casein micelles and their caseinomacropeptides: a solid-state phosphorus-31 nuclear magnetic resonance and sequence and mass spectrometric study

The phosphate sites in native ovine, caprine, and bovine casein micelles have been analyzed using sequence analysis, mass spectrometric analysis, and solid-state 31P nuclear magnetic resonance spectroscopy. Using a combination of S-ethylcysteine derivatization, sequence analysis, and mass spectrometric analysis, the phosphorylation sites of ovine (SerP151 and SerP168), caprine (SerP151 and SerP168), and bovine (SerP149) caseinomacropeptides have been localized. Various solid-state 31P methods using magic angle spinning have been applied to ascertain the local structure and dynamics of the phosphorylated serine residues and the inorganic calcium phosphates within the micelles. Contributions from the phosphorylated serine residues of kappa-CN, located in the C-terminal portion of the molecule, to the mobile constituents of the micelles were assigned by comparison with 31P nuclear magnetic resonance spectra of purified caseinomacropeptides from the various species in the dissolved state. Comparison of the 31P magic angle spinning nuclear magnetic resonance spectra of ovine, caprine, and bovine casein micelles indicates that the micelles from these species are very similar but not identical.

Binding affinity of proteins to hsp90 correlates with both hydrophobicity and positive charges. A surface plasmon resonance study

The 90 kDa heat shock protein (hsp90) is a major cytoplasmic molecular chaperone associating with numerous other proteins including steroid receptors. Here we provide the first numerical analysis of hsp90-target associations using surface plasmon resonance. Binding affinities of histones, the "native molten globule", casein and calmodulin to hsp90 decrease in the order of Kd = 70 +/- 24, 220 +/- 70 and 1800 +/- 600 nM, respectively. Analysis of the structure of binding proteins revealed that their binding affinity depends on both hydrophobicity and positive charges making the discriminative features of hsp90 similar to those of other molecular chaperones.

Structures and functionalities of milk proteins

During the last decade, marked progress has been made in the study of the fine details of the structures of milk proteins such as caseins, beta-lactoglobulin, alpha-lactalbumin, and lactotransferrin. Many of the functional properties of the individual milk proteins, as well as the milk protein products, may be described at the molecular level. This article is an attempt to thoroughly review the three-dimensional structures of major milk proteins, and to correlate them with the functional aspects of these proteins as food ingredients.

Mammary gland-specific hypomethylation of Hpa II sites flanking the bovine alpha S1-casein gene

In the lactating cow, mammary gland-specific hypomethylation occurs at two Hpa II sites in the 5'-flanking region of the alpha S1-casein gene, and one in the 3'-region. These sites, A, B and C, are at nucleotide position -1388, -774 and +18034, respectively, relative to the major transcription start site. Site B was hypomethylated when the alpha S1-casein gene was expressed, and methylated when not expressed. In transgenic mice containing the bovine alpha S1-casein 5' and 3' regulatory elements fused to the human lactoferrin (hLF) cDNA, in some cases similar methylation patterns of sites A and B, as compared to the situation in the cow, were observed. In five mouse lines (out of the seven analysed) expressing the transgene in the milk, site B was hypomethylated in the mammary gland, while it was methylated in liver. In the two other mouse lines, no correlation was found between transgene expression and mammary gland-specific hypomethylation of site B. One of the five mouse lines with transgene expression and showing mammary-gland-specific hypomethylation of site B was studied in detail. In this mouse line, induction of transgene expression preceded hypomethylation of site B.

Structure of the human kappa-casein gene

The human kappa-casein-encoding gene, Kca, was cloned and sequenced. The structural gene consists of five exons ranging from 33 to 496 nucleotides (nt) separated by introns ranging from 1146 to 2942 nt, and extends over 8821 nt. All intron/exon splice junctions conform to the GT/AG rule. The gene organization is similar to that of the bovine gene. The 5'-flanking region contains an A + T-rich sequence; TTTAATT, close to where the TATA motif is found in most other genes, a CAAT box, and an AP-1 consensus sequence. In addition, one Alu repetitive element was found in the second intron.

Action on bovine alpha s1-casein of cardosins A and B, aspartic proteinases from the flowers of the cardoon Cynara cardunculus L

The cleavage of purified bovine alpha s1-casein separately by cardosin A and cardosin B, two distinct milk-clotting aspartic proteinases (APs) present in the stigmas of the plant Cynara cardunculus L., was studied. Casein digestion peptides were separated either by SDS-PAGE or by reverse-phase HPLC, and their N-terminal amino acid sequences were subsequently determined by automated Edman degradation, thus identifying the cleavage sites. Results showed that both enzymes exert a similar but distinct action on bovine alpha s1-casein. In common they have the preference for the bond Phe23-Phe24, and the cleavage of Trp164-Tyr165 and Phe153-Tyr154. Cardosin A also cleaves the bond Tyr165-Tyr166, whereas Cardosin B cleaves an extra type of bond, Phe150-Arg151, revealing a slightly broader specificity. A model for the action of both enzymes on bovine alpha s1-casein is proposed and discussed. In comparison with the reported action of chymosin on bovine alpha s1-casein, both cardosins proved to have a broader specificity towards this particular substrate due to a higher ability to cleave bonds between residues with large hydrophobic side-chains.

Exon skipping in the ovine alpha s1-casein gene

The reported cDNA sequences for the bovine (Bos taurus) and ovine (Ovis aries) alpha s1-caseins display a high degree of identity with the exception that a 24 bp region, corresponding to bovine exon 16, is absent in the ovine sequence. Here we show that the ovine gene for alpha s1-casein contains a sequence block displaying 23/24 identity to bovine exon 16, indicating that the absence of this block from ovine mRNA is due not to genomic deletion but to exon skipping. Analysis of the products obtained by reverse transcription of ovine alpha s1-casein mRNA followed by amplification, demonstrated the presence of mRNA species containing the exon 16 sequence as well as the species in which it had been spliced out. It was estimated that the latter constitutes 20% of the total ovine alpha s1-casein mRNA. We propose that a substitution within the donor splice site is responsible for the partial skipping of exon 16, possibly through the formation of an inhibitory RNA secondary structure.

Expression of a bovine kappa-CN cDNA in the mammary gland of transgenic mice utilizing a genomic milk protein gene as an expression cassette

Transgenic mice were produced by microinjection of a DNA construct composed of the bovine kappa-casein (kappa-CN) cDNA under the control of the goat beta-CN 5' promoter elements and 3' flanking regions into pronuclear-stage embryos. The gene construct targeted the expression of bovine kappa-CN RNA to the mammary gland and secretion of bovine kappa-CN in the milk. In the three lines studied (BC-7, BC-31 and BC-67) the transgene was stably integrated and propagated as a Mendelian locus. Expression of the bovine protein in lactating mice from the three transgenic lines was demonstrated by northern and western blots. In ten different tissues analysed by northern blotting, expression was confined to the mammary gland of lactating transgenic mice from line BC-7, with low-level expression also observed in the salivary gland of lines BC-31 and BC-67. Transgene expression in the mammary gland paralleled normal casein gene expression during lactation and was not observed in virgin females. The level of bovine kappa-CN mRNA expression on day 10 of lactation in hemizygous transgenic females in relation to endogenous mRNA of whey acid protein (WAP) gene expression was 14%, 69%, and 127% in lines BC-7, BC-31 and BC-67, respectively. No association between transgene copy number and expression was observed. The bovine kappa-CN concentration in milk on day 10 of lactation ranged from 0.94 to 3.85 mg of protein per ml of milk. The bovine kappa-CN expressed in mouse milk had the same molecular mass and immunoactivity with polyclonal antibodies as did kappa-CN from bovine milk. A high degree of variation in the production of bovine kappa-CN within each of the transgenic lines was observed.

Characterization of three types of human alpha s1-casein mRNA transcripts

Here we report the molecular cloning and sequencing of three types of human alpha s1-casein transcripts and present evidence indicating that exon skipping is responsible for deleted mRNA transcripts. The largest transcript comprised 981 bp encoding a signal peptide of 15 amino acids followed by the mature alpha s1-casein sequence of 170 amino acids. Human alpha s1-casein has been reported to exist naturally as a multimer in complex with kappa-casein in mature human milk, thereby being unique among alpha s1-caseins [Rasmussen, Due and Petersen (1995) Comp. Biochem. Physiol., in the press]. The present demonstration of three cysteines in the mature protein provides a molecular explanation of the interactions in this complex. Tissue-specific expression of human alpha s1-casein was indicated by Northern-blot analysis. In addition, two cryptic exons were localized in the bovine alpha s1-casein gene.

Genotyping bovine milk proteins using allele discrimination by primer length and automated DNA sizing technology

A method for genotyping kappa-casein (A, B, E), beta-casein (A1, A2, A3, A5, B) and beta-lactoglobulin (A, B) simultaneously by the use of allele discrimination by primer length combined with automated detection of fragments with a sequencing instrument is described. Seven different mutations within the milk protein genes were analysed in order to distinguish between the alleles examined. The samples were amplified in two separate multiplex polymerase chain reactions (PCRs), which were then pooled and separated according to size in a single lane on the gel. By using stringent PCR conditions, we have been able to achieve allele-specific amplifications and minimize amplification of mis-matched primer for all seven mutations.