The concentrations and functions of many cellular proteins are regulated by the ubiquitin pathway. Cullin family proteins bind with the RING-finger protein Roc1 to recruit the ubiquitin-conjugating enzyme (E2) to the ubiquitin ligase complex (E3). Cul1 and Cul7, but not other cullins, bind to an adaptor protein, Skp1. Cul1 associates with one of many F-box proteins through Skp1 to assemble various SCF-Roc1 E3 ligases that each selectively ubiquitinate one or more specific substrates. Here, we show that Cul3, but not other cullins, binds directly to multiple BTB domains through a conserved amino-terminal domain. In vitro, Cul3 promoted ubiquitination of Caenorhabditis elegans MEI-1, a katanin-like protein whose degradation requires the function of both Cul3 and BTB protein MEL-26. We suggest that in vivo there exists a potentially large number of BCR3 (BTB-Cul3-Roc1) E3 ubiquitin ligases.
Cullins assemble the largest family of ubiquitin ligases by binding with ROC1 and various substrate receptors. CUL4 function is linked with many cellular processes, but its substrate-recruiting mechanism remains elusive. We identified a protein motif, the DWD box (DDB1-binding WD40 protein), and demonstrated the binding of 15 DWD proteins with DDB1-CUL4A. We provide evidence supporting the critical function of the DWD box and DDB1's role as the linker mediating DWD protein association with CUL4A. A database search predicts that about one-third of WD40 proteins, 90 in humans, contain the DWD box, suggesting a potentially large number of DWD-DDB1-CUL4-ROC1 E3 ligases. The ubiquitin-proteasome pathway regulates the concentration and conformation of many cellular proteins in response to changes in physiological conditions. This pathway consists of a cascade of three activities performed by E1 (ubiquitin-activating), E2 (ubiquitin-conjugating), and E3 (ubiquitin ligase) enzymes (Hochstrasser 1996;King et al. 1996;Hershko and Ciechanover 1998). A critical step in this process is how individual protein substrates are recruited to specific E3 ligases. The RING family represents the major family of E3 ligases. Members either contain an intrinsic RING finger domain (as in MDM2 and BRCA1) or bind in trans with a small RING finger protein, such as ROC1 (also known as Rbx1 and Hrt1) by the cullins, to recruit and activate an E2 (Jackson et al. 2000;Petroski and Deshaies 2005).A remarkable aspect of cullin E3 ligases is that each cullin can assemble into many distinct cullin-RING-dependent ligases (CRLs) by interacting with a conserved motif present in multiple proteins (Petroski and Deshaies 2005). To recruit specific substrates, CUL1 utilizes an N-terminal domain to bind with a linker protein, SKP1 (Feldman et al. 1997;Skowyra et al. 1997;, which does not interact with other cullins (Michel and Xiong 1998). SKP1 uses a separate domain to bind with a conserved protein motif, the F box, which, via its additional protein-protein interaction modules, recruits various substrates, often phosphorylated, to the CUL1-ROC1 catalytic core. To bring specific substrates to CUL2-and CUL5-dependent ligases, a heterodimeric linker complex containing elongins B and C binds simultaneously to an analogous N-terminal domain in CUL2 and CUL5 and to two similar protein motifs, the VHL box and SOCS box. VHL and SOCS proteins, via their additional protein-protein interaction modules, target various substrates differentially to the CUL2-ROC1 or CUL5-ROC2 catalytic cores (Kamura et al. 1998(Kamura et al. , 2001(Kamura et al. , 2004Stebbins et al. 1999;Zhang et al. 1999). Omitting a linker, CUL3 utilizes its N-terminal domain to bind to proteins with a conserved 100-residue protein motif known as a BTB domain, which, via additional protein-protein interaction domains, then target various substrates to the CUL3-ROC1 catalytic core (Furukawa et al. 2003;Geyer et al. 2003;Pintard et al. 2003;Xu et al. 2003). The presence of multiple substrate receptors-...
A subset of WD40 proteins that contain a DWD motif (for DDB1 binding WD40) is reported to act as substrate receptors for DDB1-CUL4-ROC1 (for Damaged DNA Binding 1-Cullin 4-Regulator of Cullins 1) based E3 ubiquitin ligases in humans. Here, we report 85 Arabidopsis thaliana and 78 rice (Oryza sativa) proteins containing the conserved 16-amino acid DWD motif. We show by yeast two-hybrid and in vivo coimmunoprecipitation that 11 Arabidopsis DWD proteins directly interact with DDB1 and thus may serve as substrate receptors for the DDB1-CUL4 machinery. We further examine whether the DWD protein PRL1 (for Pleiotropic Regulatory Locus 1) may act as part of a CUL4-based E3 ligase. PRL1 directly interacts with DDB1, and prl1 and cul4cs mutants exhibited similar phenotypes, including altered responses to a variety of stimuli. Moreover, AKIN10 (for Arabidopsis SNF1 Kinase Homolog 10) was degraded more slowly in cell extracts of prl1 and cul4cs than in cell extracts of the wild type. Thus, both genetic and biochemical analyses support the conclusion that PRL1 is the substrate receptor of a CUL4-ROC1-DDB1-PRL1 E3 ligase involved in the degradation of AKIN10. This work adds a large new family to the current portfolio of plant E3 ubiquitin ligases.
Limited DNA end resection is the key to impaired homologous recombination (HR) in BRCA1mutant cells. Here through a loss-of-function CRISPR screen we identify DYNLL1 as an inhibitor of DNA end resection. Loss of DYNLL1 allows DNA end resection and restores HR in BRCA1mutant cells, thereby inducing resistance to platinum drugs and poly(ADP-ribose) polymerase
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