Signal Transduction

Ras regulates assembly of mitogenic signaling complexes through the effector protein IMP. Matheny, S. A. et al. Nature 427, 256–260 (2004)

The Ras signalling cascade includes Raf, mitogen-activated protein (MAP) kinase and MAP kinase kinase (MEK). Matheny et al. have now identified IMP, a Ras effector that negatively regulates MAP-kinase activation. IMP limits the formation of Raf–MEK complexes in the absence of Ras activation. Ras signalling can inactivate IMP through auto-polyubiquitylation, which releases the inhibition of complex formation.

Replication

Identification of two origins of replication in the single chromosome of the archaeon Sulfolobus solfataricus. Robinson, N. P. et al. Cell 116, 25–38 (2004)

Archaeons have a minimal replication apparatus that resembles that of eukaryotes. Robinson et al. now show that archaeons, like eukaryotes, use multiple origins of replication. S. solfataricus has two active origins, which are recognized selectively by its three homologues of the eukaryotic initiator proteins Cdc6 and Orc1.

Development

Cup is an eIF4E binding protein required for both the translational repression of oskar and the recruitment of Barentsz. Wilhelm, J. E. et al. J. Cell Biol. 163, 1197–1204 (2003)

Drosophila Cup is an eIF4A binding protein that associates with Bruno and regulates oskar mRNA translation in oogenesis. Nakamura, A. et al. Dev. Cell 6, 69–78 (2004)

In fly oogenesis, oskar mRNA is translationally repressed until it is correctly localized to the posterior pole. Two groups have now identified Cup, a translation initiation factor 4E (eIF4E) binding protein, as a translational repressor of oskar. Wilhelm et al. also show that Cup is required to recruit the localization factor Barentsz to the oskar ribonucleoprotein complex, thereby providing a likely regulatory link between localization and translation.

Techniques

Detection of molecular interactions at membrane surfaces through colloid phase transitions. Baksh, M. M. et al. Nature 427, 139–141 (2004)

Studies of biochemical events at membrane surfaces are technically challenging. Using lipid membranes supported on a silica substrate, Baksh et al. now suggest an experimental approach that involves adjusting the lipid membrane composition so that the membrane system is close to a phase transition. Small perturbations on the membrane surface, such as molecular interactions, induce easily measurable changes in the macroscopic organization of the colloid.