CREB (cAMP-response-element-binding protein) is a transcription factor that binds to cAMP-responsive element (CRE) promoter sites to regulate the transcription of numerous genes involved in metabolic regulation, depression, long term memory, and other physiological processes. Phosphorylation on serine 133 (Ser133) activates CREB to induce transcription of target genes. Diverse stimuli such as growth factors, neurotransmitters, hypoxia, growth factors, UV light, survival signals, and stress signals are some of the known activators of CREB. Cayman’s CREB (Phospho-Ser133) Transcription Factor Assay is a non-radioactive, sensitive method for detecting CREB DNA binding activity in nuclear extracts or whole cell lysates.