The Myb family of transcription factors regulates proliferation, differentiation and apoptosis of hematopoletic cells. The avian myeloblastosis viral (v-Myb) protein is nuclear and binds to specific DNA sequences. The gene encoding for v-Myb is oncogenic, causing monoblastic leukemia and transforming myelomonocytic cells by deregulating the expression of specific target genes. v-Myb functions as a transcriptional activator, and it can repress biologically relevant genes such as Ets-2, which promotes macrophage differentiation. The proto-oncogene c-Myb encodes for a nuclear protein that plays a role in transcriptional regulation and may be essential for hematopoietic cell proliferation. A-Myb is also member of the Myb family that is expressed in proliferating B cell centroblasts. Transgenic mice overexpressing A-Myb posses enhanced hyperplasia of the lymph nodes.