DNA VARIANTS WITHIN THE 5'FLANKING REGION OF BOVINE-MILK PROTEIN-ENCODING GENES

Based on their high or low average milk protein contents during lactat ion, 1064 cows were selected. From this group, 242 cows with maximal d iffering milk protein genotype combinations were chosen for a monthly sampling of milk. These milk samples were analysed quantitatively by u sing infra-red spectroscopy and densitometry of electrophoretically se parated proteins. DNA from blood samples from 10 to 12 cows of differe nt breeds were taken for DNA sequencing of 5'flanking gene regions. Fo r some variable sites a PCR-based detection of RFLP and SSCP was carri ed out in populations. The most divergent variants in the 5'flanking r egions of each of the milk protein encoding genes were cloned in the p GL2-Basic expression vector, transfected into mammary gland cells and measured for reporter gene expression. Altogether 65 variable sites (m ore than 1% of the nucleotide positions) were found in the 5'flanking regions of milk protein encoding genes. On example of the beta-lactogl obulin encoding gene, RFLPs for five of the DNA variants revealed to b e polymorphically distributed in breeds and were closely associated wi th yield and content of beta-LG in milk. SSCP analysis of 5'flanking r egions of the other milk protein encoding genes is performed in a larg er number of cows. In cell culture rests, the promoter variants led to different reporter gene expression. Investigation of effects of singl e DNA sites on the quantity of milk proteins can be improved by furthe r rest systems.