Rap 2A

Rap2B is a 21 kDa small GTP-binding protein that that exhibits 46% identity with Ras proteins and is similarly post-translationally modified by farnesyl and palmitate groups. It colocalizes with several markers of the Golgi complex, thus indicating that its site of function was distinct from that of Rap1A. In contrast to Rap1A, Rap2B protein does not interfere with Ras-induced transformation suggesting that the activity of Rap proteins goes beyond the regulation of Ras protein function. Ras proteins provide a crucial link in the intracellular signalling cascades. Ras proteins are members of the small G protein family. These proteins are characterized by a molecular weight between 20 and 30 kDa, the ability to bind GTP or GDP and a low intrinsic GTPase activity. These proteins relay signals from the plasma membrane activated by receptor tyrosine kinases to the nucleus via a network of serine/threonine kinases. Ras proteins belong to a family of approximately 40 mammalian and 60 non-mammalian proteins. Ras proteins were first discovered as the hyperactive products of mutant Ras genes which promote cancer by disrupting the normal controls on cell proliferation and differentiation; about 30% of human cancers have mutations in a Ras gene.