Coumermycin A1, a cell permeable antibiotic, has been found to be a dimerizing agent that can activate a modified Raf-1 protein and stimulate the mitogen-activated protein kinase cascade. This compound has also been reported to induce autophosphorylation of GyrB-Janus Kinase (JAK) 2 fusion proteins, thus bypassing receptor activation. JAKs are cytoplasmic protein kinases that interact with intracellular domains of cytokine receptors which plays an important role in signal transduction. The activation of JAK is thought to induce cell proliferation. Studies suggest that Coumermycin A1 can inhibit the supercoiling activity of gyrase by binding to the gyrase B subunit.