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Egalitarian mutants that do not interact with the dynein light chain do not maintain oocyte fate. Orb (red) and synaptonemal complex (green) initially concentrate in the 'oocyte' cell but are subsequently lost.
The small GTPases Arl3p and Arl1p function sequentially to recruit diverse effector proteins to the Golgi apparatus. Similarly to ARF proteins, Arl1p is targeted to membranes by myristoylation. Arl3p, however, is not myristoylated. Recent work demonstrates that Arl3p, and its mammalian orthologue ARFRP1, are targeted to membranes by amino-terminal acetylation, which facilitates recognition by the membrane receptor Sys1p/hSys1.
The specificity of cytoskeleton-mediated cargo transport is critical for cell polarization. The Egalitarian protein — required for the localization of mRNAs and proteins to the oocyte of the Drosophila melanogaster ovary — is now reported to interact with an integral component of the dynein motor complex, the dynein light chain Dlc1.
Proteins exit the trans-Golgi network (TGN) through multiple mechanisms that are poorly understood. New work identifies FAPP1 and FAPP2 as TGN-localized proteins that regulate post-Golgi carrier formation through interactions with phosphatidylinositol 4-phosphate (PtdIns(4)P) and ARF1.
p53 can induce apoptosis through its well defined role as a regulator of transcription, but also by a less well defined transcription-independent mechanism. Two recent studies demonstrate that p53 mediates mitochondrial permeabilization through direct physical interactions with the pro-apoptotic Bcl-2 family members, Bax and Bak.
Loss of integrin-mediated attachment to the extracellular matrix triggers apoptosis through the activation of caspases. A recent study shows that disruption of integrin function also induces mitochondrial release of Bit1, a caspase-independent effector of apoptosis.
The microtubule-associated proteins MAP2 and tau are important for regulating microtubule dynamics and bundling, but can also bind to actin filaments. It seems, however, that only MAP2 can bind directly to actin filaments and, curiously, the actin-binding domain is situated within the microtubule-binding domain.