Garry P. Nolan

Cloning of the p50 DNA binding subunit of NF-κB : homology to rel and dorsal

The DNA binding subunit of the transcription factor NF-kappa B, p50, has been cloned. p50 appears to be synthesized as a larger protein that is then processed to its functional size. Sequence analysis reveals remarkable homology for over 300 amino acids at the amino-terminal end to the oncogene v-rel, its cellular homolog c-rel, and the Drosophila maternal effect gene dorsal. This establishes NF-kappa B as a member of the rel family of proteins, all of which display nuclear-cytosolic translocation. Protein sequence from the p65 polypeptide has established that it is not encoded in the same mRNA as p50. However, p65 appears homologous to c-rel, suggesting that c-rel may form heterodimers with p50 and rel may include a homodimerization motif.

DNA binding and IκB inhibition of the cloned p65 subunit of NF-κB, a rel-related polypeptide

Abstract The sequence and biochemical properties of the product of the cloned cDNA for the p65 subunit of nuclear factor κB (NF-κB) have been determined. The cDNA has an open reading frame of 549 amino acids capable of encoding a 60 kd protein. NF-κB p65 contains an amino-terminal region of 320 amino acids with extensive similarity to the oncogene c- rel and lesser similarity to NF-κB p50. In vitro translated p65 forms a DNA-binding complex with NF-κB p50, and the binding of this complex can be specifically inhibited by purified IκB. Progressive carboxy-terminal deletions of p65 show that, contrary to previous assumptions, p65 does include a DNA-binding domain that in vivo might become activated only through hetero-oligomerization with p50. DNA binding by truncated p65 is inhibited by IκB, thus mapping the IκB interaction domain to the rel -homologous region and suggesting that IκB exerts its inhibitory effect upon NF-κB primarily through interaction with p65.