FIG. 4.

The HNF-3β-specific site is required for transcriptional activation by the TTR enhancer. Constructs consisting of the TTR enhancer and –202 promoter driving the expression of the CAT gene were transfected into HepG2 cells to determine the importance of the HNF-3β-specific site in the TTR-2 region of the TTR enhancer. Transient expression levels (average from three separate transfection experiments) of the wild-type TTR enhancer containing an HNF-3β-specific site were compared with mutations that allowed recognition of all of the HNF-3 isoforms or that eliminated HNF-3 binding (None). Also included for comparison is the activity of the TTR promoter constructs that lacked the TTR enhancer region. The CMV-driven β-galactosidase plasmid was included in each transfection to normalize cellular protein extracts for differences in transfection efficiency, as described previously (51,52,56).