D-site binding protein transactivation requires the proline- and acid-richdomain and involves the coactivator p300

The D-site binding protein (DBP) is a member of the proline- and acid-rich (PAR) domain subfamily of basic/ leucine zipper proteins and is involved in transcriptional regulation in the liver. Deletion analysis of the DBP prot ein was carried out in an effort to define the function of the conserved PA R domain. Internal deletions of the protein, i.e. removing portions of the PAR domain, resulted in a substantial loss in transactivation of a high aff inity DBP reporter construct when assayed in Rep G2 cells. These same seque nces conferred significant transactivation to GAL4 DNA binding domain fusio n proteins, indicating that this region acts as part of an independent acti vation domain comprised of sequences in both the amino terminus and in the PAR domain of DBP. The coexpression of full-length expression constructs fo r both DBP and hepatic leukemia factor resulted in a dramatic increase in a ctivation mediated by the GAL4-DBP fusion proteins, suggesting the involvem ent of a regulated coactivator in this process. DBP transactivation appears to be a p300-dependent process, as a 12 S E1A expression construct disrupt ed DBP-mediated transactivation, and a p300 expression vector, but not a CR EB binding protein vector, was able to restore DBP transactivation. These r esults suggest that the PAR domain is required for DBP activation, which oc curs through a regulated, p300-dependent process.