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Institute of Genetics, University of Berne, CH-3001 Berne, Switzerland
1 E-mail: martin.braunschweig{at}itz.unibe.ch
β-Lactoglobulin (β-LG) is the major whey protein in the milk of cows and other ruminants. It is well established that the predominant genetic variants β-LG A and B are differentially expressed. Extensive investigation of the genetic variation in the promoter region of the BLG gene revealed the existence of specific haplotypes associated with the A and B variants. However, the genetic basis for the differentially expressed BLG A and B alleles is still elusive. In this study additional genetic variation further upstream in the 5'-flanking region of the BLG gene was identified, including 6 single nucleotide substitutions, a single nucleotide deletion, and a 7-bp duplication. Comparison of DNA sequences showed that the investigated 5'-flanking region is highly conserved between ruminants, and the duplication g.–1885_–1879dupCTCTCGC and the substitution g.–1888A>G are only found in the BLG A and D alleles in cattle. The cytosine at position g.–1957 and the thymines at positions g.–2008 and g.–2049 are only found in BLG B alleles of cattle. It is suggested that the described genetic variability contributes to the differential allelic expression of the BLG gene.
Key Words: β-lactoglobulin • genetic polymorphism • milk protein • expression
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