MYROSINASE-BINDING PROTEINS ARE DERIVED FROM A LARGE WOUND-INDUCIBLE AND REPETITIVE TRANSCRIPT

Several non-myrosinase proteins have been found in association with so me of the myrosinases extracted from rape (Brassica napus) seed. Most of these proteins seemed to belong to a large family of proteins rangi ng in size over approximately 30-110 kDa, namely the myrosinase-bindin g protein (MBP) family. Potentially all of these MBPs might be derived from a single large precursor, encoded by a 3.3-kb transcript. This t ranscript coded for a 99-kDa glycine-rich protein with a highly repeti tive structure. The mature 50-kDa and 52-kDa MBP amino-terminal was lo cated 255 amino acids from the putative initiation methionine. Also, a more divergently related transcript, the protein product of which was unknown, has been cloned. However, the largest open reading frame sug gested a proline-rich protein. While this transcript seemed to be expr essed predominantly in seeds, the MBP transcripts were expressed in se veral tissues and also exhibited a responsiveness to wounding and meth yl jasmonate. Both proteins exhibited significant similarities to lect ins from Artocarpus integer and from Maclura pomifera.