NFkB

(= NFkappaB)

A transcription factor (originally found to switch on transcription of genes for the kappa class of immunoglobulins in B-lymphocytes). It is involved in activating the transcription of more than 20 genes in a variety of cells and tissues. NF k B is found in the cytoplasm in an inactive form, bound to the protein I k B. A variety of stimuli, such as tumour necrosis factor, phorbol esters and bacterial lipopolysaccharide activate it, by releasing it from I k B, allowing it to enter the nucleus and bind to DNA. It has two subunits p50 and p65 that bind DNA as a heterodimer. The dimerisation and DNA binding activity are located in N-terminal regions of 300 amino acid that are similar to regions in the Rel and dorsal transcription factors.