The glucosinolate hydrolyzing enzymes myrosinase (thioglucoside glucoh
ydrolase, EC 3.2.3. 1) are encoded by a multigene family consisting of
two subgroups. The first two nuclear genes representing each of these
two subgroups of the new gene family, Myr1.Bn1 and Myr2.Bn1, from Bra
ssica napus have been cloned and sequenced. Based on conserved regions
in cDNA of three species, PCR (polymerase chain reaction) primers wer
e made, and used to amplify and characterize the structure of the myro
sinase genes in seven species of Brassiceae. Southern hybridization an
alysis of PCR products and genomic DNA indicates that myrosinase is en
coded by at least 14 genes in B. napus, with similar numbers in the ot
her species of Brassicaceae investigated' The Myr1 gene cloned from B.
napus has a 19 amino acid signal peptide and consists of 11 exons of
sizes ranging from 54 to 256 bp and 10 introns of sizes from 75 to 229
bp. The Myr2 gene has a 20 amino acid signal peptide and consists of
12 exons ranging in size from 3 5 to 262 bp and 11 introns of sizes fr
om 81 to 131 bp. The exons from the two genes have 83 % homology at th
e amino acid level. The intron-exon splice sites are of GT..AG consens
us type. The signal peptides and presence of sites for N-linked glycos
ylation, suggest transport and glycosylation through the ER-Golgi comp
lex. The differences between the two genes are discussed on the basis
of their predicted expression at different developmental stages in the
plant. Both genes show homology to a conserved motif representing the
glycosyl.hydrolase family of enzymes.