The function and specificity of the C-terminal tripeptide glyoxysomal targeting signal in Neurospora crassa

Abstract

The function of the C-terminal tripeptide targeting signal responsible for microbody targeting in many eukaryotes has been investigated in the filamentous fungus Neurospora crassa. Using an in-vivo targeting assay that employs transformants carrying C-terminally-modified versions of the bacterial enzyme chloramphenicol acetyltransferase (CAT), it has been demonstrated that C-terminal tripeptide-dependent import occurs most efficiently in response to nutritional acetate-induction. Under these conditions Neurospora generates a specialized organelle, the glyoxysome, which carries the enzymes responsible for the glyoxylate cycle and can be distinguished from peroxisome-like microbodies that contain catalase. Moreover, several C-terminal peptides have been tested in 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-terminus of the glyoxylate cycle enzyme isocitrate lyase in higher plants, does not apparently function here.