HBZ interacts with JunD and stimulates its transcriptional activity.

Human T-cell leukemia virus type I (HTLV-I) bZIP factor (HBZ) is a viral basic leucine zipper protein that was originally described as a partner of cAMP response element binding protein-2 and as a repressor of HTLV-I viral transcription. In addition, HBZ is able to interact with the activator protein-1 (AP-1) transcription factors c-Jun and JunB, the interaction with c-Jun leading to a transcriptional repression of AP-1-regulated genes. Here we show that HBZ also interacts with JunD in vitro and in vivo, and that this association occurs via the bZIP domain of the two proteins. Moreover, we show that HBZ can activate JunD-dependent transcription and that its amino-terminus is required.