CRYPTOGAM PHYTOCHROMES

Phytochrome responses in cryptogams are well characterized, However, t he properties of cryptogam phytochromes are not well understood, becau se of the difficulty in obtaining suitable material, Recent advances i n molecular biology offer the possibility of studying cryptogam phytoc hromes at the molecular level, The functional domains in cryptogam phy tochromes have been predicted from the homology of the deduced amino a cid sequences to known sequences of different functional proteins, Cry ptogam phytochrome gene families are highly variable in size and compo sition, The most structurally unusual cryptogam phytochrome, found in the moss Ceratodon and the fern Adiantum, has a protein kinase catalyt ic domain in the C-terminal half, although the N-terminal half is homo logous to conventional phytochromes, In conventional phytochrome, modu les homologous to the bacterial two-component (transmitter) protein ki nase have also been found in the C-terminal ends, While phytochromes l ack membrane-spanning sequences, some types may have microtubule attac hment sequences, The relationship of these to dichroic phytochrome is discussed, Phytochrome mRNA and proteins are also discussed, as well a s the use of mutants in elucidating signal transduction pathways.