Abstract
Six clones of monoclonal antibodies, MYC‐1 to ‐6, were prepared by using two kinds of truncated c‐myc proteins, p23 and p42, produced in Escherichia coli as immunogens. Analysis with enzyme‐linked immunosorbent assays and immunoblotting assays with peptides produced in Escherichia coli showed that 5 clones of monoclonal antibodies, MYC‐1 to ‐4 and ‐6, were reactive with c‐myc protein encoded by exon 2. The remaining one clone, MYC‐5, was reactive with the portion of c‐myc protein encoded by exon 3. All monoclonal antibodies were also reactive with phosphorylated c‐myc protein produced by insect cells infected by the baculovirus expression vector with the human c‐myc gene. With immunoblotting assays using cellular lysates, MYC‐1 and ‐3 detected bands at the levels of 58 kDa and 60 kDa, MYC‐5 detected a band at 56 kDa and MYC‐6 detected bands at 68 kDa and 75 kDa. All of these bands were detectable in nuclear extracts of HL‐60 and Colo320, both of which have amplified c‐myc genes, and also the extract of RmycYl which is the c‐myc gene transfectant into 3Y1 rat cells. None of them was detectable in peripheral blood mononuclear cells and 3Y1, both of which lacked activated c‐myc genes. This indicates that these nuclear proteins are either c‐myc gene products or molecules closely related to the c‐myc gene. The remaining two clones, MYC‐2 and ‐4, detected a band at the level of 85 kDa in cytoplasmic extracts of all the above‐mentioned cells independent of the presence of the c‐myc gene. This suggests that 85 kDa protein might be irrelevant to the c‐myc gene. The 56 kDa protein was detectable by MYC‐5 in phytohemagglutinin‐stimulated peripheral blood mononuclear cells as well as leukemic cells of some patients.
Keywords: c‐myc, Monoclonal antibody
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