The fungus Acremonium typhinum produces a novel endoprotease during sy
mbiotic endophytic infection of the grass, Poa ampla. This protease is
unusual because it is highly active in the presence of sodium dodecyl
sulfate. The enzyme is a thiol-containing serine protease and is loca
lized to a crude membrane fraction. Similar protease activity has been
detected in endophyte-infected Poa autumnalis and Poa sylvestris plan
ts. Expression of this protease may be important in endophytic infecti
on of Poa spp., because similar activity has not been detected in endo
phyte-infected Festuca arundinacea or Lolium perenne.