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. Functions as both an activator of prestalk gene expression and repressor of prespore gene expression. Binds DNA as a dimer (By similarity). Heterodimerizes with dimB; in vitro. Also able to form homodimer; in vitro. In response to DIF-1, it accumulates rapidly in the nucleus. Nuclear accumulation is dependent on dimB. Maximum levels of expression in prespore cells, but also expressed in prestalk cells at the slug stage. Developmentally regulated with levels peaking at culmination. Defective in DIF biosynthesis and in DIF-1-induced stalk-cell differentiation. Exhibits morphological and cell type differentiation defects. DimA and dimB double mutant has the same phenotype. Belongs to the bZIP family.