YY1 is a ubiquitously expressed transcription factor with fundamental roles in embryogenesis, differentiation, replication and proliferation. YY1 contains four zinc finger motifs of the Cys-Cys-His-His type and can activate different eukaryotic genes or repress different eukaryotic genes as well as regulate some viral promoters . YY1 deficient embryos die approximately at the time of implantation, suggesting that YY1 has an essential role in embryonic development. YY1 is overexpressed in cancer cells such as prostate cancer and therefore may be considered a prognostic marker .