B-myb is transcription factor involved in multiple cellular processes such as cell survival, proliferation, and differentiation. B-myb was identified in a low-stringency screen of a T-cell cDNA library probed with a C-myb probe. C-myb is a cellular proto-oncogene highly conserved in vertebrates and invertebrates. The chicken c-myb proto-oncogene was the first ortholog discovered. Investigation of the origins of the avian myeloblastosis virus (AMV) led to the discovery that the AMV genome contained transduced sequences from normal chicken cellular DNA that resulted in a viral oncogenic version (v-myb) of the c-myb gene. B-myb is cell cycle regulated and expressed in all proliferating cells. Recent studies show that it is the only myb family member detected in embryonic stem cells and is essential to cell cycle progression and genomic stability.