Glycosome assembly in trypanosomes: variations in the acceptable degeneracy of a COOH-terminal microbody targeting signal.

Trypanosomes compartmentalize most of their glycolytic enzymes in a peroxisome-like microbody, the glycosome. The specificity of glycosomal targeting was examined by expression of chloramphenicol acetyltransferase fusion proteins in trypanosomes and monkey cells. Compartmentalization was assessed by cell fractionation, differential detergent permeabilization, and immunofluorescence. The targeting signal of trypanosome phosphoglycerate kinase resides in the COOH-terminal hexapeptide, NRWSSL; a basic amino acid is not required. The minimal targeting signal is, as for mammalian cells, a COOH-terminal tripeptide related to -SKL. However, the acceptable degeneracy of the signal for glycosomal targeting in trypanosomes is considerably greater than that for peroxisomal targeting in mammals, with particularly relaxed requirements in the penultimate position.