MAFF is a basic leucine zipper (bZIP) transcription factor that lacks a transactivation domain. It is known to bind the US-2 DNA element in the promoter of the oxytocin receptor (OTR) gene and most likely heterodimerizes with other leucine zipper-containing proteins to enhance expression of the OTR gene during term pregnancy. This protein can also form homodimers, and since it lacks a transactivation domain, the homodimer may act as a repressor of transcription. Recombinant human MAFF protein, fused to His-tag at N-terminus, was expressed in E.coli