CREB (cAMP response elementbinding) proteins are transcription factors which bind to certain sequences called cAMP response elements (CRE) in DNA. Transcription factors play a key role in controlling cell proliferation, cell cycle progression, fuel metabolism and so on through changes in target gene transcription. CREB has many functions in many different organs although most of its functions have been studied in relation to the brain. CREB proteins in neurons are thought to be involved in the formation of long-term memories. CRE-BP1 is one of the most abundant CREbinding proteins. The level of its mRNA is fairly abundant in some regions of the brain such as hippocampus and is induced in the regenerating liver, suggesting that CRE-BP1 is important for both signal transduction in the brain and cellular proliferation. In the majority of patients with acute myeloid leukemia (AML), CREB was found to be overexpressed in the bone marrow and this overexpression was associated with poor prognosis. CREB5 (CRE-Bpa) consists of 508 amino acids and has a molecular weight of 56,840. CREB5 is highly homologous with CRE-BP1 in four regions: two of them are the regions containing the putative metal finger or the DNA-binding domain consisting of the basic amino acid cluster and the leucine zipper.