A cDNA clone was obtained from Arabidopsis thaliana that encodes a protein containing 92 amino acid residues with high sequence identity (57%) to bovine acyl-CoA-binding protein (ACBP). The coding sequence of this clone was expressed in Escherichia coli and the gene product (10.4 kDa) was purified. The recombinant A. thaliana ACBP (rAthACBP) was shown to bind acyl-CoA esters and protect acyl-CoAs from degradation by microsomal acyl-hydrolases. Antibodies that were raised to rAthACBP recognized the native Arabidopsis ACBP and also cross-reacted with a number of other plant ACBPs, including rapeseed (Brassica napus) ACBP. The pattern of expression and level of the gene product were examined in various tissues of Arabidopsis and Brassica using Western blotting. A. thaliana tissues contained between 3 and 143 micrograms AthACBP g(-1) FW depending on the tissue (0.4 to 14 nmol g(-1) FW). Developing B. napus seeds underwent a 12-fold increase in ACBP levels during seed maturation (20 to 250 micrograms ACBP g(-1) FW); the highest concentration occurring near the peak of triacylglycerol accumulation (26 nmol g(-1) FW.