The present invention relates to a newly identified family of protein serine/threonine kinases which phosphorylate microtubule-associated protein 2 (MAP2). It is based, in part, on the cloning and characterization of novel MAP2 kinases designated extracellular signal-regulated kinase 1, 2, and 3 (ERK1, ERK2, ERK3) which are expressed in the central nervous system, and on the identification of another ERK family member, ERK4, with antisera. The present invention provides for recombinant nucleic acid molecules and proteins representing members of the MAP2 kinase family, and also for microorganisms, transgenic animals, and cell lines comprising recombinant MAP2 kinase molecules. In additional embodiments of the invention, the present invention provides for methods for assaying cellular factor activity, including, but not limited to, nerve growth factor activity, in which the activation of MAP2 kinase serves as an indicator of cellular factor activity. These methods may be extremely useful in screening compounds for the presence of a desired cellular factor activity. In specific embodiments, compounds which may be useful in the treatment of Alzheimer's disease, peripheral neuropathies, and diabetes may be identified using the methods of the invention.