CTCF (acronym for a “CCCTC-binding factor”) is a highly conserved and ubiquitous protein with multiple functions, which include regulation of transcription, chromatin insulation, and genomic imprinting.
The CTCF protein was originally identified for its ability to bind to a promoter element of the chicken c-myc gene. The sequence recognized by CTCF contained the CCCTC repeats and therefore the protein was defined as CTCF (the CCCTC-binding factor). However, it was later discovered that other CTCF-target sequences (or CTSs) were remarkably dissimilar, and the term “multivalent transcription factor” was coined for CTCF. Another unusual feature of the CTSs is their length: the analysis of binding patterns of CTCF to multiple sites demonstrated that CTCF requires about 50–60-bp-long sequence to form a complex with DNA.