Two exons specific for the myb proto-oncogene found upstream from the avian myeloblastosis virus-transduced myb sequences.

A partial restriction map of cloned 5.42-kb chicken DNA (clone P542, Perbal et al. 1983), covering a portion of the c-myb locus, is presented. The 5' end of the v-myb gene (approximately 0.5 kb) is located at the 3' end of P542 DNA, the remainder are the cellular sequences not transduced by avian myeloblastosis virus. Two non-contiguous DNA segments were detected within these cellular sequences which code for the 5' end of c-myb mRNA. These two exons, designated e1 and e2, are separated by a approximately equal to 1.5-kb non-coding region. Both of them are transcribed into 0.4 kb located near the 5' end of c-myb mRNA. The second exon e2 (approximately equal to 0.2 kb) is flanked at its 3' end by a short non-coding region within which virus-cell recombination took place. The possible presence of a portion of this intron in the 2.1-kb v-myb mRNA is discussed.