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The Ku-binding motif is a conserved module for recruitment and stimulation of non-homologous end-joining proteins.

ABSTRACT: The Ku-binding motif (KBM) is a short peptide module first identified in APLF that we now show is also present in Werner syndrome protein (WRN) and in Modulator of retrovirus infection homologue (MRI). We also identify a related but functionally distinct motif in XLF, WRN, MRI and PAXX, which we denote the XLF-like motif. We show that WRN possesses two KBMs; one at the N terminus next to the exonuclease domain and one at the C terminus next to an XLF-like motif. We reveal that the WRN C-terminal KBM and XLF-like motif function cooperatively to bind Ku complexes and that the N-terminal KBM mediates Ku-dependent stimulation of WRN exonuclease activity. We also show that WRN accelerates DSB repair by a mechanism requiring both KBMs, demonstrating the importance of WRN interaction with Ku. These data define a conserved family of KBMs that function as molecular tethers to recruit and/or stimulate enzymes during NHEJ.

SUBMITTER: Grundy GJ

PROVIDER: S-EPMC4831024 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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The Ku-binding motif is a conserved module for recruitment and stimulation of non-homologous end-joining proteins.

Grundy Gabrielle J GJ Rulten Stuart L SL Arribas-Bosacoma Raquel R Davidson Kathryn K Kozik Zuzanna Z Oliver Antony W AW Pearl Laurence H LH Caldecott Keith W KW

Nature communications 20160411

The Ku-binding motif (KBM) is a short peptide module first identified in APLF that we now show is also present in Werner syndrome protein (WRN) and in Modulator of retrovirus infection homologue (MRI). We also identify a related but functionally distinct motif in XLF, WRN, MRI and PAXX, which we denote the XLF-like motif. We show that WRN possesses two KBMs; one at the N terminus next to the exonuclease domain and one at the C terminus next to an XLF-like motif. We reveal that the WRN C-terminal ...[more]

PMID: 27063109

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Project description:The proposal aims to characterise the pathways of DSB repair and recombination in Arabidopsis with the main focus of this research being the NHEJ pathway of illegitimate recombination. We will build on our expertise and resources in the field of DSB repair in plants, using the Arabidopsis NHEJ mutant atku80 which is an excellent model system for the study of DSB repair in higher eukaryotes (West et al., 2002 Plant J. 31, 517-28). Comparison of the transcriptome in NHEJ mutant and wild type plants under different experimental conditions will identify novel candidate genes involved in DNA DSB repair or damage signalling pathways.We will conduct 4 separate experiments on Arabidopsis seedlings grown on 0.5 MS media: the first will be a control consisting of Wassilewskija (WS-2) plants grown under standard conditions. In the second experiment WS plants will be exposed to the chemotherapeutic agent bleomycin (1 microgram per ml). This agent has been shown to cause both single and double strand breaks in the genome of Arabidopsis seedlings (Menke et al., 2001 Mut. Res. 493, 87-93). This agent is used in preference to gamma irradiation, which causes high levels of oxidative damage to cellular components. These experiments will characterise for the first time the transcriptional responses of Arabidopsis cells to the specific induction of DNA strand breaks. The transcript profile will also be determined in untreated atku80 mutants. This experiment will identify the components of novel and previously characterised DNA repair pathways up regulated in the mutant background. Finally, transcript analysis of bleomycin treated atku80 mutants and comparison with untreated mutant plants and both untreated and treated WS plants will identify novel putative DSB repair genes up regulated in response to genotoxic stress in the absence of a Ku80 mediated DSB repair pathway.The results of these studies will provide new and important information which will be instrumental in identifying novel genes and pathways involved in DNA repair and genome stability in plants and help elucidate the fundamental differences that exist between animal and plant DSB repair processes. Experiment Overall Design: Number of plants pooled:20

Project description:Classical non-homologous end joining (C-NHEJ) and homologous recombination (HR) compete to repair mammalian chromosomal double strand breaks (DSBs). However, C-NHEJ has no impact on HR induced by DNA nicking enzymes. In this case, the replication fork is thought to convert the DNA nick into a one-ended DSB, which lacks a readily available partner for C-NHEJ. Whether C-NHEJ competes with HR at a non-enzymatic mammalian replication fork barrier (RFB) remains unknown. We previously showed that conservative "short tract" gene conversion (STGC) induced by a chromosomal Tus/Ter RFB is a product of bidirectional replication fork stalling. This finding raises the possibility that Tus/Ter-induced STGC proceeds via a two-ended DSB intermediate. If so, Tus/Ter-induced STGC might be subject to competition by C-NHEJ. However, in contrast to the DSB response, where genetic ablation of C-NHEJ stimulates HR, we report here that Tus/Ter-induced HR is unaffected by deletion of either of two C-NHEJ genes, Xrcc4 or Ku70. These results show that Tus/Ter-induced HR does not entail the formation of a two-ended DSB to which C-NHEJ has competitive access. We found no evidence that the alternative end-joining factor, DNA polymerase ?, competes with Tus/Ter-induced HR. We used chromatin-immunoprecipitation to compare Rad51 recruitment to a Tus/Ter RFB and to a neighboring site-specific DSB. Rad51 accumulation at Tus/Ter was more intense and more sustained than at a DSB. In contrast to the DSB response, Rad51 accumulation at Tus/Ter was restricted to within a few hundred base pairs of the RFB. Taken together, these findings suggest that the major DNA structures that bind Rad51 at a Tus/Ter RFB are not conventional DSBs. We propose that Rad51 acts as an "early responder" at stalled forks, binding single stranded daughter strand gaps on the arrested lagging strand, and that Rad51-mediated fork remodeling generates HR intermediates that are incapable of Ku binding and therefore invisible to the C-NHEJ machinery.

Dataset Information

The Ku-binding motif is a conserved module for recruitment and stimulation of non-homologous end-joining proteins.

Publications

The Ku-binding motif is a conserved module for recruitment and stimulation of non-homologous end-joining proteins.

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