The principal components of the protein fraction in pony mare's milk have been successfully identified and partially characterized using proteomic tools. Skimmed pony mare's milk was fractionated by either reversed phase-high-performance liquid chromatography (RP-HPLC) on a C4 column or a bi-dimensional separation technique coupling RP-HPLC in the first dimension and sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) in the second dimension (two-dimensional RP-HPLC/SDS-PAGE). The fractions thus obtained were analyzed by Edman N-terminal microsequencing and mass determination, with or without tryptic digestion, on a matrix-assisted laser desorption/ionization-time of flight spectrometer. Based on the sequence and molecular mass information obtained, identifications were achieved through a protein database search using homology or pattern research algorithms. This methodological approach was shown to be rapid, efficient and reliable in identifying the principal proteins in pony mare's milk. kappa-, alpha(s1)-, alpha(s2)-, and beta-casein, lysozyme C, alpha-lactalbumin and beta-lactoglobulin I and II were thus identified. alpha(s1) and beta-caseins displayed polymorphic patterns, probably due to alternative splicing processes leading to casual exon skipping events involving exons 7 and 14 in alpha(s1)-casein and exon 5 in beta-casein. Edman N-terminal microsequencing over 35 amino acid residues, for pony alpha(s1)-casein, clearly demonstrated the occurrence, in Equidae, of a splicing pattern similar to that reported in rodents, characterized by the constitutive outsplicing of exon 5. Pony mare's milk SDS-PAGE and RP-HPLC patterns were compared with those obtained for other milks (cow, goat and human), as were the relative levels of caseins and major whey proteins in these milks. Our results provide further evidence to support the notion that Equidae milk is closer to human breast milk than milk from bovine and caprine with respect to the casein and lysozyme C contents and casein/whey proteins ratio.

SummaryUsing SDS-polyacrylamide gel electrophoresis and rocket immunoelectrophoresis, 3 new alleles, designated a,,-Cn'-, α s1 -Cn F and α s1 -Cn o , were identified at the goat a!-Cn locus, in addition to alleles <2,j-Cn!, as!-Cn° and <2,j-Cn! previously reported by B OULANGER et al. (1984). Alleles a,,-Cn', a,,-Cn' and <2,j-Cn! are associated with a high content of a,,-casein (approximate mean contribution of each allele being 3.6 g/I) compared to ( Y ,,-Cn' with a low content (0.6 g/I) and a,,-Cn° with an intermediate content (1.6 g/1) ; a,,-Cn° appears to be a true null allele. In a sample of 213 Alpine females from 49 flocks in West Central France, the frequencies of the 6 alleles were : <2,j-Cn! = 0.14 ; a,,-Cn° = 0.05 ; <2,j-Cn! = 0.01 ; ot,,-Cn' = 0.34 ; a,,-Cn F = 0.41 ; and a, i -Cn° = 0.05. In a sample of 159 Saanen females from 52 flocks of the same region, the frequencies were : <2,j-Cn! = 0.07 ; <2,j-Cn! = 0.06 ; < 2 ,j-Cn<' = 0 ; a 'I -CnB-= 0.41 ; a,,-Cn' ! 0.43 ; <2,j-Cn'" = 0.03. Additional data confirm that loci a, I -Cn and a,,-Cn are closely linked.Preliminary investigations indicated a significant superiority in casein content of milks from goats possessing the allele <2,j-Cn!, as compared to that of milks from goats of genotypes (xs,-Cn F / / <2,j-Cn! and <2,j-Cn! /a 'I -Cn F and, in a large herd (N = 251), a strong correlation was observed between the a,,-casein content and the rennet-casein content of milk (r = 0.68 ; b = 0.64).

SummaryUsing SDS-polyacrylamide gel electrophoresis and rocket immunoelectrophoresis, 3 new alleles, designated a,,-Cn'-, α s1 -Cn F and α s1 -Cn o , were identified at the goat a!-Cn locus, in addition to alleles <2,j-Cn!, as!-Cn° and <2,j-Cn! previously reported by B OULANGER et al. (1984). Alleles a,,-Cn', a,,-Cn' and <2,j-Cn! are associated with a high content of a,,-casein (approximate mean contribution of each allele being 3.6 g/I) compared to ( Y ,,-Cn' with a low content (0.6 g/I) and a,,-Cn° with an intermediate content (1.6 g/1) ; a,,-Cn° appears to be a true null allele. In a sample of 213 Alpine females from 49 flocks in West Central France, the frequencies of the 6 alleles were : <2,j-Cn! = 0.14 ; a,,-Cn° = 0.05 ; <2,j-Cn! = 0.01 ; ot,,-Cn' = 0.34 ; a,,-Cn F = 0.41 ; and a, i -Cn° = 0.05. In a sample of 159 Saanen females from 52 flocks of the same region, the frequencies were : <2,j-Cn! = 0.07 ; <2,j-Cn! = 0.06 ; < 2 ,j-Cn<' = 0 ; a 'I -CnB-= 0.41 ; a,,-Cn' ! 0.43 ; <2,j-Cn'" = 0.03. Additional data confirm that loci a, I -Cn and a,,-Cn are closely linked.Preliminary investigations indicated a significant superiority in casein content of milks from goats possessing the allele <2,j-Cn!, as compared to that of milks from goats of genotypes (xs,-Cn F / / <2,j-Cn! and <2,j-Cn! /a 'I -Cn F and, in a large herd (N = 251), a strong correlation was observed between the a,,-casein content and the rennet-casein content of milk (r = 0.68 ; b = 0.64).

The polymorphism of caseins, a-lactalbumin and β-lactoglobulin was investigated in African Bos taurus (N'Dama, Baoulé, Kuri) and Bos indicus (Shuwa Arab, Sudanese Flzlani) populations. The respective frequencies of alleles a sl-Cn B and a sl-Cn c in the N'Dama (0.89 and 0.11) and Baoulé (0.92 and 0.08) breeds were almost opposite to those found in the Shuwa Arab zebu (0.22 and 0.78), a true zebu, which confirms a phenomenon already documented in the literature. Because the a sl-Cn B , / 3-Cn Al ,

This paper describes the elucidation of the primary structure of the three genetic variants of goat asl-casein, asl-Cn D, E and F, which have been found to be associated with reduced amounts of asl-casein in milk. Variant E has the same electrophoretic mobility as variant B, but differs from the latter by the substitutions of Arg for Lys and of Thr for Ala at positions 100 and 195. A genetically controlled event which does not affect the amino acid sequence of this variant might be responsible for its lower rate of synthesis compared to that of asl-casein B. The deletion of 11 amino acids at positions 59 -69 and of 37 amino acids at positions 59 -95 in variant B leads to variants D and F. In both cases the deletions, which start at the same position of the polypeptide chain, include the major phosphorylation site of the protein. On the basis of sequence data for casein genes and cDNAs, it was concluded that the deletions occurring in the D and F variants are due to the exclusion of one and several exons, respectively. The observed deletions in the proteins could thus be the consequence of splice site mutations which would induce altered RNA processing and hence reduce the rate of synthesis of the casein.Early work on the casein family, which includes three phosphoproteins, asl-, as2-, and fl-casein, and one glycophosphoprotein, k--casein, was performed on proteins isolated from cow's milk. The primary structures of these four polypeptides, which contain 169 -209 amino acid residues, have already been established [l]. Whereas genetic polymorphism is widespread for asl-, fl-, and k--casein, it is more restricted and is breed-dependent for as2-casein [2, 31. Segregation studies led to the conclusion that the four proteins are controlled by a cluster of closely linked genes. In this cluster no recombination was observed in a total of 448 informative families [4]. The unit of inheritance is thus the haplotype which is a combination of individual alleles of each of the four clustered loci.Although the same classes of caseins have been identified in goat's milk [5], so far, in this species, only asl and as2-casein are known to exhibit genetic polymorphism [6]. Segregation studies have confirmed that asl-and as2-casein genes are closely linked suggesting that, as in the cow, casein expression in the goat is controlled by a cluster of genes.Electrophoretic patterns of goat asl-casein are unusually complex due to differences in the mobilities of different variants and to varying intensities of electrophoretic bands which reflect different amounts of protein [6]. It is now established [6, 71 that polymorphism of asl-casein is under the control of at least seven alleles denoted as: asl-CnA, asl-CnB, asl-Cnc, asl-CnD, asl-Cn", asl-CnF and asl-Cno. Alleles asl-CnA, asl-