A CYTOKININ-BINDING PROTEIN COMPLEX FROM TOBACCO-LEAVES - THE 57 KDA SUBUNIT HAS HIGH HOMOLOGY TO S-ADENOSYL-L-HOMOCYSTEINE HYDROLASE

A cytokinin binding protein complex (CBP130) has been purified from to bacco leaves (Nicotiana sylvestris). It contains two protein species o f 57 and 36 kDa (CBP57 and CBP36). The cDNAs encoding CBP57 have been isolated from a tobacco cDNA library. Their predicted amino acid seque nces showed significant homology between CBP57 and S-adenosyl-L-homocy steine (SAH) hydrolase, which catalyzes the reversible hydrolysis of S AH, a methyltransferase inhibitor. A combination of gel filtration and western blot analysis revealed that both CBP57 and benzyladenine (BA) -binding activity were eluted at a peak of 130 kDa. A purified CBP130 fraction contains SAH hydrolase activity. We discuss possible CBP57 as a cytokinin receptor subunit and its possible role as a regulator of methylation.