Maize cap1 encodes a novel SERCA-type calcium-ATPase with a calmodulin-binding domain

A cDNA (CAP1) isolated from maize roots shares sequence identity with genes encoding P-type Ca2+-ATPases and restores the growth phenotype of yeast mu tants defective in Ca2+-pumps. CAP1 was transcribed and translated in the y east mutant. Furthermore, the membrane-integrated product formed a Ca2+-dep endent phosphorylated intermediate and supported Ca2+ transport. Although C AP1 shares greater sequence identity with mammalian "endoplasmic reticulum- type" Ca2+-pumps, it differs from these genes by having features of calmodu lin (CaM)-regulated Ca2+-pumps. CAP1 from yeast microsomes bound CaM, and t he CAP1-dependent Ca2+ transport in yeast was stimulated by CaM. Peptides f rom the C terminus of CAP1 bound CaM. Anti-CAP1 antibodies specifically rec ognized a maize microsomal polypeptide that also bound CaM. A similar polyp eptide also formed a Ca2+-dependent phosphoenzyme. Our results suggest that cap1 encodes a novel form of CaM-regulated Ca2+-ATPase in maize. CAP1 appe ars to be encoded by one or two genes in maize. CAP1 RNA is induced only du ring early anoxia, indicating that the Ca2+-pump may play an important role in O-2-deprived maize cells.