THIOLASE MESSENGER-RNA TRANSLATED INVITRO YIELDS A PEPTIDE WITH A PUTATIVE N-TERMINAL PRESEQUENCE

Thiolase is part of the fatty acid oxidation machinery which in plants is located within glyoxysomes or peroxisomes. In cucumber cotyledons, proteolytic modification of thiolase takes place during the transfer of the cytosolic precursor into glyoxysomes prior to the intraorganell ar assembly of the mature enzyme. This was shown by size comparison of the in vitro synthesized precursor and the 45 kDa subunit of the homo dimeric glyoxysomal form. We isolated a full-length cDNA clone encodin g the 48 539 Da precursor of thiolase. This plant protein displayed 40 % and 47% identity with the precursor of fungal peroxisomal thiolase a nd human peroxisomal thiolase, respectively. Compared to bacterial thi olases, the precursor of the plant enzyme was distinguished by an N-te rminal extension of 34 amino acid residues. This putative targeting se quence of cucumber thiolase shows similarities with the cleavable pres equences of rat peroxisomal thiolase and plant peroxisomal malate dehy drogenase.