ZEATIN-BINDING PROTEIN INVOLVED IN THE ACTIVATION OF IN-VITRO RNA-SYNTHESIS BY TRANS-ZEATIN - ISOLATION FROM BARLEY LEAF CYTOSOL

A procedure for isolating a protein with high affinity for the natural ly occurring cytokinin trans-zeatin from the barley leaf cytosol was d eveloped. Along with gel filtration and hydrophobic chromatography, th is procedure involved affinity chromatography using trans-zeatin immob ilized on Epoxy-activated Sepharose. The high affinity for zeatin in p rotein with mol wt of 67 +/- 2 kD was demonstrated by its competition with antibodies against trans-zeatin in the competitive-binding ELISA system when trans-zeatin was immobilized on polystyrene microtiter pla tes. When assayed in direct-binding ELISA and by Western-blot analysis , the protein cross-reacted with anti-idiotypic antibodies isolated fr om anti-zeatin serum. In the in vitro system containing barley chromat in and RNA polymerase I, the isolated protein enhanced RNA synthesis e longation in the presence of trans-zeatin. Data obtained permitted us to consider the isolated protein as a receptor for the naturally occur ring cytokinin trans-zeatin, which mediated transcription activation w ith this phytohormone.