A full-length cDNA of 1951 bp encoding a calnexin (CNX) protein was cloned from a Pisum
sativum expression library. The open reading frame (ORF) within this cDNA encodes a 551-amino acid
protein with a calculated molecular mass of 62.47 kDa that exhibits extensive homology with the CNX
proteins from soybean (80%), Arabidopsis thaliana (70%), maize (70%), and dog (39%). The characteristic
CNX signature motifs, KPEDWDE and GXW, generally found in molecular chaperones, are present in pea
CNX (PsCNX), along with putative sites for Ca2+ binding and phosphorylation. In PsCNX, a signal
sequence and a single transmembrane domain are also present at the N- and C-terminal ends, respectively.
The PsCNX protein is expressed constitutively at the RNA level in vegetative and flowering tissues, as was
evident from Northern analysis. Expression of PsCNX was light independent. In vitro translation of PsCNX
cDNA yielded a 75-kDa precursor, which, in the presence of canine microsomal membranes, was
cotranslationally processed into a 72.5-kDa product and was imported and localized to the endoplasmic
reticulum.
