Control of in vitroTranscription Exerted by the Cytokinin Receptor

We developed systems of in vitrotranscription comprising chromatin or nuclei from barley leaves of various ages and from Arabidopsis thalianaleaves. We isolated a protein with a mol wt of 67 kD from both plant species. In the presence of cytokinin, this protein enhanced the elongation of RNA synthesis in both in vitrosystems. The effect of 67-kD protein depended on the presence of a specific hormone. The effect of a hormone–receptor complex on transcription in the system containing chromatin and RNA polymerase I from barley leaves of various ages was consistent with the effect of cytokinin on transcription in the intact leaves of various ages. A combination of the 67-kD receptor protein from A. thalianaleaves and trans-zeatin enhanced transcription in the system from barley leaves, and reciprocally, the 67-kD protein from barley leaves induced a cytokinin-dependent transcription activation in the system from A. thalianaleaves. This evidence indicates the absence of species specificity of the cytokinin receptor. A cytokinin-dependent activation of protein kinase activity of the 67-kD protein from barley leaves was demonstrated.