A recombinant expression plasmid was constructed by inserting the cDNA encoding mature receptor-associated protein (RAP) into pGEX vector. High level intracellular expression of the RAP gene was Observed in the DH5a bacteria transformed with the recombinant pGEX vector after IPTG induction. The abundant GST fusion protein constituted 39. 4 % the total cellular protein. The fusion proteins were purified from bacterial lysates by using GST-Sepharose 4B affinity chromatography. The Western blot analysis showed that the rabbit anti-RAP antiserum recognized an apparent mass of 44 ku band from rat kidney microvillar protein. The high level expression and rapid purification of RAP-GST fusions was discussed.