A quantitative trait locus (QTL) affecting milk fat percentage has been mapped 
to the centromeric end of the bovine chromosome 14 (BTA14). This genomic area 
includes the DGAT1 gene, which encodes acyl-CoA:diacylglycerol acyltransferase 
1, the key enzyme of triglyceride biosynthesis. Genetic and biochemical studies 
led to the identification of the nonconservative DGAT1-K232A polymorphism as a 
causal mutation for the QTL. In addition to this, another polymorphism in the 
5'-regulatory region of this gene, the DGAT1 variable number of tandem repeat 
(VNTR), also showed a strong association with milk fat percentage. This promoter 
VNTR polymorphism affects the number of potential Sp1 binding sites and 
therefore might have an impact on DGAT1 expression and also milk fat content. 
Hence, the DGAT1 VNTR polymorphism might be another causal mutation for the 
BTA14 QTL. However, evidence for Sp1 binding to this polymorphic site and for 
the capability of DGAT1 VNTR alleles to stimulate gene expression was lacking. 
In the current work Sp1-VNTR interactions were analyzed by EMSA. In addition, 
effects of DGAT1 VNTR alleles on gene expression were measured with reporter 
gene analyses. Conclusions from the results are that 1) the DGAT1 VNTR sequence 
is indeed a target for Sp1 binding; 2) DGAT1 VNTR alleles can stimulate gene 
expression in vitro and probably in vivo as well; and 3) although the 
stimulating effects of the different DGAT1 VNTR alleles did not show significant 
differences in vitro, their effects on transcription might be different in the 
chromatin context existing in vivo.