Transcriptional regulator involved in DIF-1 signaling. DIF-1 (Differentiation Inducing Factor-1) is a signal molecule involved in the differentiation of pstO (prestalk-O) cells (By similarity). May be a direct activator of ecmA. Binds DNA as a dimer (By similarity). Heterodimerizes with dimA; in vitro. Also able to form homodimer; in vitro. In response to DIF-1, it accumulates rapidly in the nucleus. Developmentally regulated with levels peaking at culmination. Following starvation, development proceeds normally only until the finger stage, when extremely long and thin fingers/slugs are produced. DimA and dimB double mutant has the same phenotype. Belongs to the bZIP family.