Nuclear factor kappa B (NF-kappaB) is a ubiquitous transcription factor and an essential mediator of gene expression during activation of immune and inflammatory responses. NF-kappaB mediates the expression of a great variety of genes in response to extracellular stimuli. NF-kappaB associates with IkappaB proteins in the cell cytoplasm, which inhibit NF-kappaB activity. IkappaB is phosphorylated by IkappaB kinase (IKK) complex that contains IKKalpha, IKKbeta, and IKKgamma. A novel molecule that associates with and activates IKK was recently identified and designated CIKS (for connection to IKK and SAPK/JNK) and Act1 (for NF-kappaB activator 1). CIKS directly interacts with IKKgamma. CIKS/Act1 also activates activating transcription factor (ATF) and activator protein 1 (AP-1) through Jun kinase (JNK). These results indicate that CIKS/Act1 is involved in the inflammation and stress responses. CIKS/Act1 is ubiquitously expressed in human tissues.