The cJun proto-oncogene was first identified as the cellular homolog of the avian sarcoma virus vjun oncogene. JunB and JunD have been shown to be almost identical to cJun in their C terminal regions, which are involved in dimerization and DNA binding, whereas their N terminal domains, which are involved in transcriptional activation, diverge. JunB is a transcription factor involved in regulating gene activity following the primary growth factor response. It binds to the DNA sequence 5'-TGA[CG]TCA-3'.