Abstract
COP9 signalosome (CSN) is an 8-subunit nuclear protein complex. Null mutations for CSN results in lethality, indicating its essential role in development. To date, enzymatic activity has been detected in CSN to deconjugate Rub1 from E3 ubiquitin-ligases, which then modulates activity of ubiquitin-proteasome degradation pathway.
Functional dissection of mammalian CSN revealed that N-terminal portion of CSN1 (CSN1N) represses activated signals of the SAPK/JNK1 signaling pathway. CSN1N also reduces accumulation of JNK1, leading to suppression of c-Jun phosphorylation. To analyze this regulation, we have isolated proteins directly binding to CSN1N (NBPs). NBPs cover a novel spectrum of proteins, including SAP130, DDX15/hPrp43/mDEAH9, CFIm68, which are components of transcription/RNA processing complexes.
We have isolated the Arabidopsis NBP orthologs and its knockout plants. Detailed biochemical analyses on CSN-NBP interactions together with in planta research should reveal this novel mechanism of CSN. Here we discuss the complex interaction between CSN, COP/DET/FUS, and their interacting partners.
