protein kinase C conserved region 1 (C1 domain) found in B-Raf (Rapidly Accelerated Fibrosarcoma) kinase and similar proteinsSerine/threonine-protein kinase B-Raf, also called proto-oncogene B-Raf, p94, or v-Raf murine sarcoma viral oncogene homolog B1, activates ERK with the strongest magnitude, compared with other Raf kinases. Mice embryos deficient in B-Raf die around midgestation due to vascular hemorrhage caused by apoptotic endothelial cells. Mutations in B-Raf have been implicated in initiating tumorigenesis and tumor progression, and are found in malignant cutaneous melanoma, papillary thyroid cancer, as well as in ovarian and colorectal carcinomas. Most oncogenic B-Raf mutations are located at the activation loop of the kinase and surrounding regions; the V600E mutation accounts for around 90% of oncogenic mutations. The V600E mutant constitutively activates MEK, resulting in sustained activation of ERK. B-Raf is a mitogen-activated protein kinase kinase kinase (MAP3K, MKKK, MAPKKK), which phosphorylates and activates 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.