No abstract

The a s1 -casein (a s1 -Cas) locus in the goat is characterized by a polymorphism, the main feature of which is to be qualitative as well as quantitative. A systematic analysis performed in an autochthon southern Italy breed identified a new rare allele (M), which was characterized at both the protein and genomic level. The M protein displays the slowest electrophoretic mobility of the a s1 -Cas variants described so far. MS and automated Edman degradation experiments showed that this behavior was due to the loss of two phosphate residues in the multiple phosphorylation site (64S This was confirmed by sequencing a genomic DNA fragment encompassing exon 9 where the 8th codon (TCG) was shown to be mutated to TTG. Sequencing of amplified genomic DNA segments spanning the 5¢ and 3¢ flanking regions of each exon allowed us to identify 23 single nucleotide polymorphisms and two insertion/deletion events in the coding as well as the noncoding regions. A comparison of specific haplotypes defined for each of the a s1 -CasF, A and M alleles indicates that the M allele probably arises from interallelic recombination between alleles A and B 2 , followed by a C fi T transition at nucleotide 23 of the ninth exon. The region encompassing the recombination break point was putatively located between nucleotide 86 upstream and nucleotide 40 downstream of exon 8. Interallelic recombination therefore appears to be a possible means of generating allelic diversity at the a s1 -Cas locus, at least in the goat. The previously proposed molecular phylogeny must now be revised, possibly starting from two ancestral allelic lineages.

Five ovine a sl -casein variants (A-E) were identified in an Italian population sample using gel electrophoresis at alkaline pH, gel isoelectric focusing, two dimensional gel electrophoresis, and immunoblotting with polyclonal antibodies against a s] -casein. Each casein sample produced two peaks by fast reversed-phase HPLC. Gel isoelectric focusing and electrospray mass spectrometry were used to demonstrate that the first HPLC peak contained the 191 residue a sl -casein molecular species and the second the 199 residue species, in proportions of ~ 20:80. Only in the case of the sample containing a sl -casein CE was the method for the separation of the single short and long forms of each variant unsuccessful. Both two dimensional electrophoresis followed by staining with polyclonal antibodies against

The effects of sheep αs1-casein CC, CD and DD genotypes on milk composition and cheese yield were studied. Processed bulk milk was collected from three groups of 15 ewes, carrying αs1- casein CC, CD and DD genotypes. CC milk was higher in casein content than CD or DD milk (+3·5 and +8·6% respectively), and had a higher protein[ratio ]fat ratio and a smaller casein micelle diameter. In addition, DD milk had a significantly lower αs1-casein content. The main differences were in curd formation: CC milk had better renneting properties. Cheesemaking trials, carried out in a pilot plant, showed that CC milk had better cheesemaking characteristics than DD milk, while CD milk was intermediate. Both 1 d old and fully ripened cheeses had different fat[ratio ]dry matter ratios and αs1-I-casein electrophoretic mobilities: these were lower for DD cheese. As a consequence, these genotypes could be considered as markers of milk and/or cheese quality.