CONSERVED SEQUENCE MOTIFS IN PLANT S-ADENOSYL-L-METHIONINE-DEPENDENT METHYLTRANSFERASES

Plant S-adenosyl-L-methionine-dependent methyltransferases (SAM-Mtases ) are the key enzymes in phenylpropanoid, flavonoid and many other met abolic pathways of biotechnological importance. Here we compiled the a mino acid sequences of 56 SAM-Mtases from different plants and perform ed a computer analysis for the conserved sequence motifs that could po ssibly act as SAM-binding domains. To date, genes or cDNAs encoding at least ten distinct groups of SAM-Mtases that utilize SAM and a variet y of substrates have been reported from higher plants. Three amino aci d sequence motifs are conserved in most of these SAM-Mtases. In additi on, many conserved domains have been discovered in each group of O-met hyltransferases (OMTs) that methylate specific substrates and may act as sites for substrate specificity in each enzyme. Finally, a diagramm atic representation of the relationship between different OMTs is pres ented. These SAM-Mtase sequence signatures will be useful in the ident ification of SAM-Mtase motifs in the hitherto unidentified proteins as well as for designing primers in the isolation of new SAM-Mtases from plants.