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Mechanistic basis for the spatiotemporal assembly of the Bloom Syndrome complex on ultrafine DNA bridges

ABSTRACT: The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves DNA replication and recombination intermediates, as well as mitotic DNA intertwinements, yet how its diverse activities are regulated remains unclear. Here, we identify key determinants of stable assembly of the BTRR complex on ultrafine DNA bridges (UFBs). We reveal that the RMI1-RMI2 subcomplex acts as a molecular reader of hydrophobic-rich short linear motifs (SLiMs) embedded within PICH and FANCM, thereby providing a conserved mechanism for engaging distinct Superfamily2 DNA translocases during chromosome segregation and DNA repair. During UFB resolution, SLiM binding stabilises the PICH-BTRR complex assembly and supports essential interactions among BLM, PICH, and DNA. Persistent PICH-BTRR complex association post-mitosis would compromise interphase DNA damage responses and is prevented by active PICH nuclear exclusion. Our findings define the molecular basis of UFB-binding complex assembly and highlight its spatiotemporal control required to specialise BTRR complex functions.

INSTRUMENT(S):

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Graeme Benstead-Hume

LAB HEAD: Jyoti Choudhary

PROVIDER: PXD081930 | Pride | 2026-07-30

REPOSITORIES: Pride

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			Action	DRS
	Req283-TMT_labelling_scheme.xlsx	Xlsx
	Req283-UA-Pines.msf	Msf
	Req283-UA-Pines.pdResult	Other
	Req283-UA-Pines_01.raw	Raw
	Req283-UA-Pines_02.raw	Raw

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Centromere protection requires strict mitotic inactivation of the Bloom syndrome helicase complex

Project description:The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves various DNA replication and recombination intermediates to suppress genome instability. Alongside PICH, they target mitotic DNA intertwinements, known as ultrafine DNA bridges, facilitating chromosome segregation. Both BLM and PICH undergo transient mitotic hyper-phosphorylation, but the biological significance of this remains elusive. Here, we uncover that during early mitosis, multiple protein kinases act together to strictly constrain BTRR complex activities at centromeres. Mechanistically, CDK1 destabilises the complex and suppresses its association with PICH at the chromatin underneath kinetochores. Inactivating the BLM and TOP3A interaction compromises the UFB-binding complex mitotic functions and can prevent centromere destruction. We further unravel how different mitotic phosphorylation sites of BLM affect its interaction with the TOP3A/RMI1/RMI2 subcomplex and centromeric DNA unwinding. Furthermore, we show that multiple PLK1-mediated phosphorylation on BLM is required to suppress aberrant centromere unwinding. However, notably, unleashing such activity after sister-chromatid cohesion loss facilitates separation of entangled chromosomes. Together, our study defines a centromere protection pathway in human mitotic cells, heavily reliant on a tight spatiotemporal control of the BTRR complex.

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Centromere protection requires strict mitotic inactivation of the Bloom syndrome helicase complex

Project description:The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves various DNA replication and recombination intermediates to suppress genome instability. Alongside PICH, they target mitotic DNA intertwinements, known as ultrafine DNA bridges, facilitating chromosome segregation. Both BLM and PICH undergo transient mitotic hyper-phosphorylation, but the biological significance of this remains elusive. Here, we uncover that during early mitosis, multiple protein kinases act together to strictly constrain the BTRR complex for the protection of centromeres. Mechanistically, CDK1 destabilises the complex and suppresses its association with PICH at the chromatin underneath kinetochores. Inactivating the BLM and TOP3A interaction compromises the UFB-binding complex mitotic functions and can prevent centromere destruction. We further unravel how different clusters of mitotic phosphorylation on BLM affect its interaction with the TOP3A/RMI1/RMI2 subcomplex and illegitimate centromere unwinding. Furthermore, we identify specific phosphorylation sites targeted by the MPS1-PLK1 axis functioning to prevent BLM hyper-activation at centromeres. Notably, unleashing such activity after sister-chromatid cohesion loss facilitates separation of entangled chromosomes. Together, our study defines a centromere protection pathway in human mitotic cells, heavily reliant on a tight spatiotemporal control of the BTRR complex.

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Project description:The BTRR (BLM/TOP3A/RMI1/RMI2) complex resolves various DNA replication and recombination intermediates to suppress genome instability. Alongside PICH, they target mitotic DNA intertwinements, known as ultrafine DNA bridges, facilitating chromosome segregation. Both BLM and PICH undergo transient mitotic hyper-phosphorylation, but the biological significance of this remains elusive. Here, we uncover that during early mitosis, multiple protein kinases act together to strictly constrain the BTRR complex for the protection of centromeres. Mechanistically, CDK1 destabilises the complex and suppresses its association with PICH at the chromatin underneath kinetochores. Inactivating the BLM and TOP3A interaction compromises the UFB-binding complex mitotic functions and can prevent centromere destruction. We further unravel how different clusters of mitotic phosphorylation on BLM affect its interaction with the TOP3A/RMI1/RMI2 subcomplex and illegitimate centromere unwinding. Furthermore, we identify specific phosphorylation sites targeted by the MPS1-PLK1 axis functioning to prevent BLM hyper-activation at centromeres. Notably, unleashing such activity after sister-chromatid cohesion loss facilitates separation of entangled chromosomes. Together, our study defines a centromere protection pathway in human mitotic cells, heavily reliant on a tight spatiotemporal control of the BTRR complex.

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