We developed systems of in vitro transcription comprising chromatin or nucl
ei from barley leaves of various ages and from Arabidopsis thaliana leaves.
We isolated a protein with a mol wt of 67 kD from both plant species. In t
he presence of cytokinin, this protein enhanced the elongation of RNA synth
esis in both in vitro systems. 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. thaliana leaves and trans-zeatin enhanced t
ranscription in the system from barley leaves, and reciprocally the 67-kD p
rotein from barley leaves induced a cytokinin-dependent transcription activ
ation in the system from A. thaliana leaves. This evidence indicates the ab
sence of species specificity of the cytokinin receptor. A cytokinin-depende
nt activation of protein kinase activity of the 67-kD protein from barley l
eaves was demonstrated.