Differential expression of bovine beta-lactoglobulin A and B promoter variants in transiently transfected HC11 cells

Quantification of beta-lactoglobulin A and B in the milk of heterozygous an imals has revealed a differential content of these two variants. Nucleotide sequence analysis of the first 733 bp of the bovine beta-lactoglobulin pro moter has indicated the presence of ten polymorphic sites, nine of them bei ng allele A and B specific mutations. To study the differential expression of these alleles, constructs containing 753 bp long fragments of the bovine beta-lactoglobulin A and B associated promoters mere used in transient tra nsfection experiments in HC11 cells. A differential transcription activity directed by the A and B specific promoters was consistently observed. The r elative expression levels were 57% for beta-lactoglobulin A and 43% for bet a-lactoglobulin B promoters. An allele-specific mutation has been reported to have a differential binding affinity to the activator protein-2 between the beta-lactoglobulin A and B promoters. However, experiments in HC11 cell s where the activator protein-2 binding sites were mutated in both beta-lac toglobulin A and B promoters showed no major differences in activity betwee n the mutated and native promoters.