The preferred AtSBT1.1 cleavage site within the recognition motif for proAtPSK4 is somewhat unconventional, because the di-basic residues are usually in the P1 and P2 positions, immediately upstream (on the N-terminal side) of the cleavage site (Barr, 1991) , The only caveat we have about the site is that it was identified from the cleavage product of a short fluorogenic peptide representing the putative subtilase recognition site. Other structural features of the intact Table 1 .