ISOLATION AND CHARACTERIZATION OF A CYTOKININ-BINDING PROTEIN FROM ETIOLATED MAIZE SEEDLINGS

A cytokinin-binding protein (CBP) was isolated from etiolated maize (Z ea mays L.) seedlings by two protocols. Ammonium sulfate fractionation , hydrophobic chromatography on Toyopearl HW-60, and affinity chromato graphy on immobilized trans-zeatin were used for CBP isolation accordi ng to the first protocol. The second protocol included a combination o f ion-exchange chromatography and gel filtration followed by affinity chromatography on zeatin riboside-Toyopearl as in the first protocol. In order to remove proteins that could be nonspecifically bound to the affinity matrix, chromatography on adenosine-Toyopearl preceded chrom atography on zeatin riboside-Toyopearl. Following these procedures, a CBP with a molecular weight of 70 kD was isolated. This protein specif ically and reversibly bound dihydrozeatin and, in the presence of tran s-zeatin, activated in vitro RNA synthesis in a system containing chro matin-bound RNA polymerase I from barley leaves. The protein cross-rea cted with anti-idiotypic antibodies isolated from antizeatin serum, an d, therefore, these antibodies could be considered antibodies to zeati n-binding protein. The data thus obtained indicate that the isolated C BP is a cytokinin receptor.