Identification of two normal bcr gene products in the cytoplasm.

A monoclonal antibody (7C6) has been derived against a synthetic bcr peptide and used to study normal bcr gene products. The expression of a bcr phosphoprotein of 130 kd was demonstrated, in addition to the previously identified bcr phosphoprotein of 160 kd. Sequential immunoprecipitation demonstrated that both p160 and p130 had determinants from two separate regions of the putative bcr translated sequence. The synthesis of bcr products in Philadelphia positive and negative cells was examined by metabolic labelling and it was shown that the rate of synthesis of the p210 bcr-abl product was comparable with that of the normal bcr products. The in vivo phosphorylation of the p160 exceeded that of the p130 and both normal products were unaffected by the increased phosphorylation of the p210 bcr-abl. There was no evidence with the 7C6 antibody of any normal bcr products larger than 160 kilodaltons. Immunofluorescence analysis by conventional and confocal microscopy identified normal bcr products as cytoplasmic proteins with relatively high expression in the myeloid cell line KGl.