Isolation and characterization of a fourth Arabidopsis thaliana G-box-binding factor, which has similarities to Fos oncoprotein.

A fourth member of the Arabidopsis G-box-binding factor (GBF) family of bZIP proteins, GBF4, has been isolated and characterized. In a manner reminiscent of the Fos-related oncoproteins of mammalian systems, GBF4 cannot bind to DNA as a homodimer, although it contains a basic region capable of specifically recognizing the G-box and G-box-like elements. However, GBF4 can interact with GBF2 and GBF3 to bind DNA as heterodimers. Mutagenesis of the leucine zipper of GBF4 indicates that the mutation of a single amino acid confers upon the protein the ability to recognize the G-box as a homodimer, apparently by altering the charge distribution within the leucine zipper.