Biochemical evidence that phytochrome of the moss Ceratodon purpureus is a light-regulated protein kinase

The phytochrome gene of the moss Ceratodon purpureus (phyCer) codes for a novel phytochrome polypeptide with a predicted molecular mass of 145 kDa that has a COOH-terminal domain which is homologous to the catalytic domain of eukaryotic protein kinases. In this paper we report the first biochemical evidence that in fact, as predicted from the gene sequence, PhyCer represents an active, light-regulated protein kinase. In vitro phosphorylation experiments with protonemata extracts revealed the existence of a 140 kDa protein, phosphorylated in a red/far-red light dependent manner. The binding of a polyclonal antibody directed to the protein kinase catalytic domain of PhyCer enhanced the phosphorylation of a 140 kDa band when assayed in a renaturation-auto-phosphorylation experiment with nitrocellulose bound protein. These findings strongly implicate that the phyCer gene product has protein kinase activity and is capable of auto-phosphorylation. The results of the renaturation-phosphorylation experiments were essentially the same, no matter whether protein extracts from light grown or dark adapted moss protonemata were used. Thus, phyCer expression most likely is not light regulated.