ANALYSIS OF A NOVEL CDNA-ENCODING A C219-REACTIVE PEPTIDE ISOLATED FROM METHOTREXATE-SELECTED MULTIDRUG-RESISTANT HUMAN LEUKEMIC-CELLS

We have isolated and sequenced a novel cDNA clone (D320), from methotr exate-selected multidrug-resistant (MDR) human leukemic CCRF-CEM cells , which encodes a peptide reactive with monoclonal antibody (mAb) C219 . Despite having been cloned using this ostensibly P-glycoprotein-spec ific mAb, clone D320 has no significant homology with either the MDR-e ncoding gene or, at the amino acid (aa) level, with its product, P-gly coprotein. A putative C219-binding site has been identified in D320, w hich differs at two positions from the 6-aa C219 epitope previously de scribed in P-glycoprotein.