NFkB is formed through the association of multiple subunits, either as a homodimer or heterodimer. Subunits have been identified as p50 (NFkB1), p65 (RelA), c-Rel, RelB and p52 (NFkB2). The classic NFkB form exists as a p50-p65 heterodimer and predominates in many cell types. Many of the possible combinatorial forms of homo- and heterodimers have been identified and growing evidence indicates that different forms of NFkB have different functions in cells. Interestingly, both the p50 and p52 subunits are derived from the precursor proteins p105 and p100 respectively, that each contain multiple copies of the so called ankyrin repeat at their C termini. Nuclear translocation of NFkB is confirmed by the use of electrophorectic mobility shift assays or by immunoblotting with nuclear extracts. The subunit composition of NFkB is confirmed by the use of antibodies that "supershift" the DNA/protein complex.