Characterisation of the alleles encoding ovine beta-lactoglobulins A and B.

beta-Lactoglobulin (BLG) is the major whey protein in the milk of ruminants and is produced in the mammary gland during pregnancy and lactation. Here, we compare the nucleotide sequences of two BLG-encoding clones isolated from a sheep genomic library. The two clones are very similar differing by only 1 bp in their coding regions, giving rise to a Tyr/His difference in the gene product, and suggesting that the two clones correspond to A and B allelic variants of BLG. The isoelectric points (pI) of BLGs A and B were estimated as 5.7 and 6.0, respectively. Transgenic mice carrying a particular clone secrete BLG of the expected pI into their milk. Restriction fragment length polymorphism analysis of a small sheep population demonstrated the existence of at least four BLG haplotypes.