Isolation of a protein with cytokinin‐receptor properties by means of anti‐idiotype antibodies

Abstract
A protein from cytosol of 10‐day‐old barley leaves with cytokinin‐receptor properties was isolated and 12 000‐fold purified by anti‐idiotype antibodies from anti‐BA serum. Cytokinin‐binding properties of this protein were demonstrated by its competition with Abba for immobilized BA in competitive ELISA. In the presence of BA the protein activates in vitro rRNA synthesis in the transcription elongation system containing chromatinbound RNA‐polymerase 1 from barley leaves. The protein with similar properties was isolated from barley leaf cytosol with BA‐Sepharose. The control proteins isolated with adenine‐ and ethanolamine‐Sepharose did not possess cytokinin‐binding properties and had no effect on RNA synthesis in vitro.