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Aberrant Low Expression Level of Bovine ß-Lactoglobulin Is Associated with a C to A Transversion in the BLG Promoter Region

Institute of Genetics, University of Berne, CH-3001 Berne, Switzerland

¹ Corresponding author: martin.braunschweig{at}itz.unibe.ch

ß-Lactoglobulin (ß-LG) is the major whey protein in cow’s milk. It is well established that the predominant 2 genetic variants, ß-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, respectively. However, the genetic basis for the differential expression of BLG A and B alleles is still elusive. We have previously reported a quantitative ß-LG B variant, characterized by a very low ß-LG protein expression level. Here, we report that the corresponding BLG allele (BLG B*) shows a correspondingly low mRNA expression level. Comparative DNA sequencing of 7,670 bp of the BLG B* allele and the established BLG B allele revealed a unique difference of a C to A transversion at position 215 bp upstream of the translation initiation site (g.-215C>A). This mutation segregated perfectly with the differential phenotypic expression in a paternal half-sib family and could be confirmed in 2 independent cases. The sequence of the BLG B allele in the region of the mutation is highly conserved among 4 related ruminant species. The site of the mutation corresponds to a putative consensus-binding sequence for the transcription factors c-Rel and Elk-1 as predicted by searching the TRANSFAC database. The ß-LG B* site might be relevant in the natural production of milk of low ß-LG content.

Key Words: ß-lactoglobulin • genetic polymorphism • milk protein • expression

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