GTPases: a family of molecular switches and clocks.

Members of the GTPase superfamily share a core domain with a conserved three-dimensional structure and a common GTPase cycle, but perform a wide variety of regulatory tasks in eukaryotic cells. Evolution has created functional diversity from the conserved GTPase structure in two principal ways: (i) by combining in the product of a single gene the core GTPase domain attached to one or more additional folded domains; (ii) by building around a core GTPase an assembly of proteins encoded by different genes. Analysis of the patterns of conserved amino acid side chains on surfaces of G alpha proteins reveals interfaces with other proteins in the G-protein signal linking device.