G-box (CCACGTGG) like sequences are present in a variety of plant promoters and in many cases they have been demonstrated to be required for maximal expression of the corresponding gene. A nuclear protein, GBF, interacts specifically with the G-box motif of several RBCS and CAB promoters. Here we describe the isolation of a cDNA from Arabidopsis thaliana that encodes a protein, designated GBF-1, with DNA binding properties similar to GBF. GBF-1 is characterized by a basic/leucine zipper motif which is strikingly similar to the wheat protein identified as HBP-1. GBF-1 also interacts with an oligonucleotide derived from the wheat histone 3 promoter containing the binding site (hexamer, TGACGT) for HBP-1. This DNA element also contains a G-box-like motif, modification of which results in loss in binding of GBF-1.