protein kinase C conserved region 1 (C1 domain) found in A- and C-Raf (Rapidly Accelerated Fibrosarcoma) kinases, and similar proteinsThis group includes A-Raf and C-Raf, both of which are serine/threonine-protein kinases. A-Raf, also called proto-oncogene A-Raf or proto-oncogene A-Raf-1, cooperates with C-Raf in regulating ERK transient phosphorylation that is associated with cyclin D expression and cell cycle progression. Mice deficient in A-Raf are born alive but show neurological and intestinal defects. A-Raf demonstrates low kinase activity to MEK, compared with B- and C-Raf, and may also have alternative functions other than in the ERK signaling cascade. It regulates the M2 type pyruvate kinase, a key glycolytic enzyme. It also plays a role in endocytic membrane trafficking. C-Raf, also known as proto-oncogene Raf-1 or c-Raf-1, is ubiquitously expressed and was the first Raf identified. It was characterized as the acquired oncogene from an acutely transforming murine sarcoma virus (3611-MSV) and the transforming agent from the avian retrovirus MH2. C-Raf-deficient mice embryos die around mid-gestation with increased apoptosis of embryonic tissues, especially in the fetal liver. One of the main functions of C-Raf is restricting caspase activation to promote survival in response to specific stimuli such as Fas stimulation, macrophage apoptosis, and erythroid differentiation. Both A- and C-Raf are mitogen-activated protein kinase kinase kinases (MAP3K, MKKK, MAPKKK), which phosphorylate and activate MAPK kinases (MAPKKs or MKKs or MAP2Ks), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. They function in the linear Ras-Raf-MEK-ERK pathway that regulates many cellular processes including cycle regulation, proliferation, differentiation, survival, and apoptosis. Raf proteins contain a Ras binding domain, a zinc finger cysteine-rich domain (C1), and a catalytic kinase domain. This model describes the C1 domain. The C1 domain is a cysteine-rich zinc binding domain that does not bind DNA nor possess structural similarity to conventional zinc finger domains; it contains two separate Zn(2+)-binding sites.