CHARACTERIZATION OF A NEW MYROSINASE IN BRASSICA-NAPUS

A full-length cDNA clone defining the new myrosinase gene family MC in Brassica napus was isolated and sequenced. Southern hybridization sho wed that the MC family probably consists of 3 or 4 genes in B. napus. MC genes are expressed in the developing seed, but not in the vegetati ve tissues investigated. In situ hybridizations to developing seeds sh owed that the MC genes are expressed in the myrosin cells of the embry o axis and the cotyledons. Complexes with myrosinase and myrosinase-bi nding protein (MBP) were purified and characterized. Sequencing of pep tides from myrosinases occurring in the complexes showed that the 70 k Da myrosinase is encoded by the MC genes, whereas the 65 kDa myrosinas e is encoded by the MB genes. This is in contrast to the 75 kDa myrosi nase which occurs in free form and is encoded by the MA genes. Deglyco sylations of the myrosinase complexes and the free myrosinase showed t hat the molecular sizes of the myrosinases could be reduced significan tly by this treatment, and that the size differences between the diffe rent myrosinases are mainly due to differences in glycosylation.