Family of retrovirus-associated DNA sequences (v-rel) originally isolated from an avian reticuloendotheliosis virus strain. The proto-oncogene rel (c-rel) codes for a subcellular (nuclear and cytoplasmic) transcription factor that has a role in lymphocyte differentiation. Translocation or overexpression of c-rel or competition from v-rel causes oncogenesis. The human rel gene is located at 2p12-13 on the short arm of chromosome 2.