Octamer-binding transcription factor The octamer-binding protein is a transcription factor that binds specifically to the octamer motif (ATTTGCAT)[<cite idref="PUB00053855"/>] of immunoglobulin promoters and activates these genes. There are two Ig octamer-binding proteins, designated NF-A1 and NF-A2. NF-A1 is found in all cell types, while NF-A2 is found only in lymphoid cells. The sequences of these proteins contain a region that correponds closely to the DNA-binding homeobox domains and POU transcription factors.