Antibodies directed against a bacterial fusion protein that contains the domain encoded by the highly evolutionarily conserved 5' one-third of the v-myb oncogene of avian myeloblastosis virus (AMV) detect the protein products of various members of the myb gene family. Immunoprecipitation or immunoblot analyses with these antibodies yielded the following information. First, the products of the v-myb oncogenes of AMV (p48v-myb) and of E26 virus (p135gag-mybets) contain this highly conserved amino acid sequence, as previously hypothesized. Second, p75c mYb, the product of the chicken c-myb protooncogene, also contains this protein domain. Third, these antibodies have identified the products of the human, murine, and Drosophila c-myb genes, which were all found to be nuclear proteins of Mr 75,000-80,000. The human c-myb protein product is present in immature cells of the erythroid, myeloid, and lymphoid lineages.

Nuclei obtained from chicken leukemic myeloblasts transformed by avian myeloblastosis virus were fractionated into various subnuclear compartments, which were then analyzed by specific immunoprecipitation for the presence of the leukemogenic product, p48v-myb, of the viral oncogene. In cells labeled for 30 or 60 min with L-[35S]methionine and in unlabeled exponentially dividing leukemic cells analyzed by Western blotting, p48v-myb was detected within the nucleoplasm (29 +/- 9% [standard deviation] of the total), chromatin (7 +/- 4%), and lamina-nuclear matrix (64 +/- 9%). Also, in myeloblasts analyzed by immunofluorescence during mitosis, p48v-myb appeared to be dispersed through the cell like the lamina-nuclear matrix complex. Strong attachment to the nuclear matrix-lamina complex suggests that p48v-myb may be involved in DNA replication or transcription or both.