CLONING AND CHARACTERIZATION OF A WOUNDING-INDUCED ANALOG OF THE CHAPERONE CALNEXIN FROM HELIANTHUS-TUBEROSUS

The full-length nucleotide sequence of a Jerusalem artichoke (Helianth us tuberosus L.) tuber mRNA, expressed after tissue wounding, is repor ted. The mRNA encodes a polypeptide of 540 amino acid residues with a calculated molecular mass of 61,273 Da which was identified, by sequen ce comparison, as a calnexin analog. Positional amino acid identity wi th Various animal calnexins is 39-46%. The encoded protein shows the t ypical repeats of the highly conserved A and B domains found in the ca lreticulin and calnexin proteins, and the protein expressed in Escheri chia coli was recognized by an anti-rat calreticulin antibody. Seconda ry structure prediction suggest's a similar overall membrane topology for the animal and the plant calnexin with a transmembrane domain near the C-terminus and a short acidic C-terminal domain extending in the cytoplasm. While calnexin is generally considered to be constitutive, the message of this form which is barely detectable in quiescent tuber is strongly induced after slicing and aeration of the tissue.