Proteolytic activity of the plum pox potyvirus NIa-protein on excess of natural and artificial substrates in Escherichia coli.

The plum pox potyvirus (PPV) NIa protease expressed from a medium copy number plasmid was able to process an excess of substrate expressed from a high copy number plasmid, in a binary Escherichia coli expression system. The delta B7 NIa protease mutant only partially processed the NIb-CP junction but its efficiency was independent of the amount of substrate. The delta B7 mutant essentially did not recognize an artificial cleavage site which was quite efficiently recognized by the wild-type protease. No competitive inhibition of the proteolytic activity by the presence of excess of different protease mutants was observed.