JUN is the putative transforming gene of avian sarcoma virus 17. It encodes a protein (Jun proto-oncogene, AP-1 transcription factor subunit) which is highly similar to the viral protein, and which interacts directly with specific target DNA sequences to regulate gene expression. JUN is intronless and is mapped to 1p32-p31, a chromosomal region involved in both translocations and deletions in human malignancies.