Binds to the G-box motif (5'-CCACGTGG-3') of the rbcS-1A gene promoter. G-box and G-box-like motifs are cis-acting elements defined in promoters of certain plant genes which are regulated by such diverse stimuli as light-induction or hormone control. DNA-binding heterodimer. Interacts with GBF4 (PubMed:8146148). Interacts with BZIP16 and BZIP68 (PubMed:18315949). A number of isoforms are produced. According to EST sequences. Present only in dark grown leaves and roots. Belongs to the bZIP family.