THE STRUCTURE AND FUNCTION OF PHYTOCHROME-A - THE ROLES OF THE ENTIREMOLECULE AND OF ITS VARIOUS PARTS

Phytochrome A is readily cleavable by proteolytic agents to yield an a mino-terminal fragment of 66 kilodalton (kDa), which consists of resid ues 1 to approximately 600, and a dimer of the carboxy-terminal 55-kDa fragment, from residue 600 or so to the carboxyl terminus. The former domain, carrying the tetrapyrrole chromophore, has been studied exten sively because of its photoactivity, while less attention has been pai d to the non-chromophoric portion until quite recently. However, the e vidence gathered to date suggests that this domain is also of great im portance. We present here a review of the structure and the biochemica l and physiological functions of the two domains, of parts of these do mains, and of the cooperation between them.