A family of novel basic leucine zipper proteins binds to seed-specification elements in the carrot Dc3 gene promoter

We used a yeast one-hybrid system to isolate genes encoding proteins that bind to the embryo-specification and ABA-responsive elements in the promoter of the carrot lea-class gene Dc3. Thirteen positive clones were isolated from the screen of a GAL4-cDNA hybrid library prepared from sunflower immature seed RNA. Characterization of the cDNAs showed that one of them encoded a novel protein designated DPBF-3 (Dc3 Promoter-Binding Factor-3); the remaining twelve were identical to the previously described DNA binding proteins, DPBF-1 and 2 (Kim et al., 1997). DPBF-3 is a basic leucine zipper (bZIP) protein that is very similar to DPBF-1 and 2 in their shared basic region. Isolation of DPBF-3 suggests that a small family of bZIP transcription factors are involved in the seed-specific and ABA-responsive expression of the Dc3 gene. Both phylogenetic analysis and DNA-binding studies indicated that DPBFs belong to a novel class of bZIP factors that may potentially be global regulators of seed-specific and ABA-inducible genes.