c-Jun is a protein that in humans is encoded by the JUN gene. c-Jun in combination with c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only later rediscovered as the product of the c-jun gene. It is activated through double phosphorylation by the JNK pathway but has also a phosphorylation-independent function. c-jun knockout is lethal, but transgenic animals with a mutated c-jun that cannot be phosphorylated (termed c-junAA) can survive.
This gene is the putative transforming gene of avian sarcoma virus 17. It encodes a protein that is highly similar to the viral protein, and that interacts directly with specific target DNA sequences to regulate gene expression. This gene is intronless and is mapped to 1p32-p31, a chromosomal region involved in both translocations and deletions in human malignancies.