Structure and transcription of the cellular homolog (c-myb) of the avian myeloblastosis virus transforming gene (v-myb).

We isolated and characterized molecular clones containing the chicken cellular homolog (c-myb) of the avian myeloblastosis virus oncogene (v-myb). Mapping of the c-myb clones using restriction endonucleases and hybridization to radiolabeled v-myb probes revealed that the sequences homologous to v-myb are contained within four separate regions, which have since been shown by nucleotide sequencing (Klempnauer et al., Cell 31:453-463, 1982) to carry seven exons. Analysis of c-myb transcripts showed the presence of several large precursor RNAs in addition to the 4.0-kilobase cytoplasmic mRNA. We also determined the approximate positions of the c-myb sequences that are present in the 4.0-kilobase c-myb mRNA but not present in v-myb. Some of these sequences are found in a separate region 5' to the v-myb-related sequences, whereas the remainder appear to be located immediately 3' to the v-myb-related sequences. The data presented here, in conjunction with nucleotide sequence analysis (Klempnauer et al., Cell 31:453-463, 1982), indicate that the c-myb gene contains at least eight exons which span a total of about 16 kilobase pairs. The presence of exon sequences in c-myb outside the regions of homology with v-myb raises the possibility that the v-myb and c-myb gene products may differ significantly.