HBP-1 is a sequence-specific DNA-binding protein that interacts with the hexameric sequence ACGTCA, the putative cis-acting element of the wheat histone H3 gene. Gel mobility shift and DNase I footprint analyses showed that this protein interacts with homologous sequences in the regulatory regions for the transcription of the cauliflower mosaic virus (CaMV) 35S RNA and nopaline synthase (NOS) genes, evidence that HBP-1 may bind to hexameric sequences in the regulatory regions of various genes. An HBP-1-like protein, indistinguishable from wheat HBP-1 in its the DNA-binding specificity, is present in sunflower nuclear extract, an indication that HBP-1-like DNA-binding proteins also exist in dicots.