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 facto r 1 (HNF1) binding site, responsible for most of the enhancing activit y. No differences in the migrating properties were found between this new site and the two other HNF3 sites recently described in this enhan cer. Factor HNF1 strongly inhibits binding of the HNF3 factor in this newly characterized site. The two factors were never detected simultan eously on the DNA fragment, even when their respective concentrations were modified. Competition persisted after enlarging by 5 and 10 nucle otides 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 li mited mismatching appears to modulate the interaction between transcri ptional proteins and DNA and allows a second transcriptional protein t o interplay with the former one. (C) 1995 Academic Press, Inc.