THE FUNCTION AND SPECIFICITY OF THE C-TERMINAL TRIPEPTIDE GLYOXYSOMALTARGETING SIGNAL IN NEUROSPORA-CRASSA

The function of the C-terminal tripeptide targeting signal responsible for microbody targeting in many eukaryotes has been investigated in t he filamentous fungus Neurospora crassa. Using an in-vivo targeting as say that employs transformants carrying C-terminally-modified versions of the bacterial enzyme chloramphenicol acetyltransferase (CAT), it h as been demonstrated that C-terminal tripeptide-dependent import occur s most efficiently in response to nutritional acetate-induction. Under these conditions Neurospora generates a specialized organelle, the gl yoxysome, which carries the enzymes responsible for the glyoxylate cyc le and can be distinguished from peroxisome-like microbodies that cont ain catalase. Moreover, several C-terminal peptides have been tested i n this system to extend the tripeptide targeting consensus to A/C/G/S- H/K/Q/R-I/L/V. However, the tripeptide analogue, ARM, found at the C-t erminus of the glyoxylate cycle enzyme isocitrate lyase in higher plan ts, does not apparently function here.