INTERPLAY BETWEEN A NEW HNF3 AND THE HNF1 TRANSCRIPTIONAL FACTORS IN THE DUCK HEPATITIS-B VIRUS ENHANCER

We identified a new hepatocyte nuclear factor 3 (HNF3) binding site in the DHBV enhancer. This site is close to the hepatocyte nuclear factor 1 (HNF1) binding site, responsible for most of the enhancing activity. No differences in the migrating properties were found between this new site and the two other HNF3 sites recently described in this enhancer. Factor HNF1 strongly inhibits binding of the HNF3 factor in this newly characterized site. The two factors were never detected simultaneously on the DNA fragment, even when their respective concentrations were modified. Competition persisted after enlarging by 5 and 10 nucleotides the space between the two sites. On the contrary, when the HNF3 binding site was changed into the perfect consensus site, binding of the HNF3 factor was not inhibited any longer by HNF1 and a supershift, corresponding to the binding of both factors, was observed. Thus a limited mismatching appears to modulate the interaction between transcriptional proteins and DNA and allows a second transcriptional protein to interplay with the former one. (C) 1995 Academic Press, Inc.