P105 is the precursor of the p50 subunit of the nuclear factor NF-kappa-B, which binds to the kappa-B consensus sequence 5'-GGRNNYYCC-3', located in the enhancer region of genes involved in immune response and acute phase reactions. The precursor protein itself does not bind to DNA. Active NF-kappa-B is a heterodimer of an about 50 kDa DNA-binding subunit and the weak DNA-binding subunit p65. Two heterodimers might form a labile tetramer. Nuclear, but also found in the cytoplasm in an inactive form complexed to an inhibitor (I-kappa-B). The C-terminus of p105 might be involved in cytoplasmic retention, inhibition of DNA-binding by p50 homodimers, and/or transcription activation. While translation occurs, the particular unfolded structure after the GRR repeat promotes the generation of p50 making it an acceptable substrate for the proteasome. This process is known as cotranslational processing. The processed form is active and the unprocessed form acts as an inhibitor (I kappa B-like), being able to form cytosolic complexes with NF-kappa B, trapping it in the cytoplasm. Complete folding of the region downstream of the GRR repeat precludes processing (By similarity). S-nitrosylation of Cys-66 affects DNA binding. Extended N-terminus. Wrong genetic code used for translating the sequence.