Extracellular signal-regulated kinase 2 (ERK2/p42) is also known as mitogen-activated protein kinase 1 (MAPK1). ERK2 is part of a signal transduction pathway that begins with the small GTPase Ras and continues through a cascade of protein kinases that include Raf and MEK. Activation of this signaling pathway influences many cellular processes such as proliferation, differentiation and survival. ERK2 is very similar in sequence to ERK1/p44 and the activities of both ERK1 and ERK2 are usually considered together as total ERK activity. More recent evidence has shown that ERK1 and ERK2 are not functionally redundant and may have very different and specific roles.