CHARACTERIZATION OF A PROTEIN THAT BINDS TO AT-RICH DNA IN A SEED NUCLEAR EXTRACT OF WINGED BEAN [PSOPHOCARPUS-TETRAGONOLOBUS (L.) DC. CV ISHIGAKI-4]

The organ-specific and temporally regulated expression of the genes fo r Kunitz chymotrypsin inhibitor-3 in winged bean is known to be govern ed by its 5' flanking region. Two nuclear factors that bind to AT-rich sequences in this region were detected in gel retardation assays. The binding activity of one of these factors, band 1-forming factor, was inhibited by phosphorylation, as is the AT-binding protein ATBP-1 of t obacco, which functions as an activator of transcription. In addition, the binding of band 1-forming factor was reduced in the presence of a low concentration of the minor groove-binding dye, Hoechst 33258, sug gesting that band 1-forming factor recognizes the minor groove of-the probe, as does ATBP-1. The binding of another factor, band 3-forming f actor, was also reduced by Hoechst 33258, but the binding activity of this factor was not: affected by phosphorylation. During partial purif ication by gel-filtration and affinity chromatography, the binding act ivity of band 3-forming Factor was cofractionated with a 75-ku (kDa) D NA-binding protein. These results indicate that band 3-forming factor is a new DNA-binding factor that recognizes the minor groove of AT-ric h DNA.