NF- k B pathway GENIA version. NF-kB pathway GENIA version is comprised of 16 entities, which are organized as 10 reactions. A brief explanation of the pathway is as follows: p65 binds to p50 to form a complex NF-kB (R1). NF-kB binds to IkBa in the cytosol (R2) that is rapidly phosphorylated on serine 32 and 36 (R3), ubiquitinated (R4), and degraded by 26S proteasome (R5). Freed NF-kB translocates to the nucleus (R6) and initiates the transcription of genes by binding to the kB site in their promoter region (R7). Because either IKBA or NFKB1 has a kB site in its promoter, NF-kB transcribes it to produce protein IkBa (R8) or p105 (R9), respectively. p105 is a precursor of p50 and constitutively processed to produce p50 (R10). The number of evidence sentence supporting the reaction is shown in parenthesis next to the ID of a reaction. P: phosphorylated, S: serine, Ub: ubiquitinated.