Summary Nedd4-1 is a ‘Neuronal Precursor Cell Expressed and Developmentally Downregulated Protein’ and among the most abundant E3 ubiquitin ligases in mammalian neurons. In analyses of conventional and conditional Nedd4-1 deficient mice, we found that Nedd4-1 plays a critical role in dendrite formation. Nedd4-1, the serine/threonine kinase TNIK, and Rap2A form a complex that controls Nedd4-1-mediated ubiquitination of Rap2A. Ubiquitination by Nedd4-1 inhibits Rap2A function, which reduces the activity of Rap2 effector kinases of the TNIK family and promotes dendrite growth. We conclude that a Nedd4-1/Rap2A/TNIK signaling pathway regulates neurite growth and arborization in mammalian neurons.

The cytM gene for cytochrome c w was previously found in Synechocystis sp. PCC 6803. Northern blotting analysis revealed that the cytM gene was scarcely expressed under normal growth conditions but its expression was enhanced when cells were exposed to low temperature or high-intensity light. By contrast, the expression of the genes for cytochrome c T and plastocyanin was suppressed at low temperature or under highintensity light. These observations suggest that plastocyanin and/ or cytochrome c T , which are dominant under non-stressed conditions, are replaced by cytochrome c w under the stress conditions. z 1999 Federation of European Biochemical Societies.