ABSTRACT
A main function of small G-proteins is to organize the assembly of highly ordered multiprotein complexes of signal transduction, particularly at membranes. G-proteins are regulatory guanosine triphosphateases playing a central role in signal processing. One distinguishes between heterotrimeric G-proteins, which are almost exclusively coupled to transmembrane receptors, and monomeric G-proteins with molecular masses between 16 and 36 kDa. Thus, the temporal and spatial control of PLCε activity provides an illustrative example of the targeting function of small G-proteins. To perform its organizing effect on signal transduction Ras interacts with effector proteins, recruiting them to the membrane where they come in contact with receptors and other partners. The classical example of a morphogenetic Ras–Rapidly Accelerated Fibrosarcom–Mitogen-Activated Protein kinase cascade is provided by the development of photoreceptor cells in the Drosophila eye. The ommatides of the insect's compound eyes are composed of eight different types of photoreceptor cell inducing each other during embryogenesis.
