CCAAT-enhancer-binding proteins (or C/EBPs) is a family of transcription factors composed of six members, named from C/EBPα to C/EBPζ. They promote the expression of certain genes through interaction with their promoters. Once bound to DNA, C/EBPs can recruit so-called co-activators (such as CBP) that in turn can open up chromatin structure or recruit basal transcription factors.
C/EBP proteins interact with the CCAAT (cytosine-cytosine-adenosine-adenosine-thymidine) box motif, which is present in several gene promoters. They are characterized by a highly conserved basic-leucine zipper (bZIP) domain at the C-terminus. This domain is involved in dimerization and DNA binding, as are other transcription factors of the leucine zipper domain-containing family (c-Fos and c-jun). The bZIP domain structure of C/EBPs is composed of an α-helix that forms a "coiled coil" structure when it dimerizes. Members of the C/EBP family can form homodimers or heterodimers with other C/EBPs and with other transcription factors, which may or may not contain the leucine zipper domain. The dimerization is necessary to enable C/EBPs to bind specifically to DNA through a palindromic sequence in the major groove of the DNA. C/EBP proteins also contain activation domains at the N-terminus and regulatory domains.
These proteins are found in , adipocytes, hematopoietic cells, spleen, kidney, brain, and many other organs. C/EBP proteins are involved in different cellular responses, such as in the control of cellular proliferation, growth and differentiation, in metabolism, and in immunity. Nearly all the members of the C/EBP family can induce transcription through their activation domains by interacting with components of the basal transcription apparatus. (C/EBPγ is an exception that lacks a functional transcriptional activation domain.) Their expression is regulated at multiple levels, including through hormones, mitogens, cytokines, nutrients, and other factors.