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Ertl da Costa, J.

Publications and source records attributed to Ertl da Costa, J..

2 recordsLinked to original sources
bioRxiv2026

Structures and molecular mechanisms of RAD54B in modulating homologous recombination

Genome stability is essential for cellular viability yet constantly threatened by endogenous and exogenous DNA-damaging agents. Among these, DNA double-strand breaks (DSBs) are particularly harmful and in S/G2 phases are faithfully repaired through homologous recombination (HR), a high-fidelity pathway utilising homologous sequences in sister chromatin. The RAD51 recombinase forms nucleoprotein filaments on single-stranded DNA (ssDNA) to mediate homology search, strand invasion and subsequent D-loop formation that leads to DNA synthesis and repair. The efficiency of HR depends on precise regulation of RAD51 filament dynamics by accessory factors, including RAD54 and RAD54B, which belong to the SWI2/SNF2-family DNA translocases. While RAD54 is well-characterized, RAD54Bs molecular functions remain poorly understood. Here, we define RAD54Bs role in HR using cryo-electron microscopy, mutagenesis, biochemical and cellular assays. We show that RAD54B stabilizes RAD51-DNA filaments, inhibits RAD51 ATPase activity, and promotes strand invasion, D-loop formation and strand exchange. The N-terminal domain (NTD) alone supports filament stabilization and strand exchange, while the C-terminal ATPase domain is required for D-loop formation. Structural and biochemical analyses reveal three RAD51-interacting sites within the NTD and a unique domain ({beta}-domain) that bridges RAD51 protomers and contacts donor dsDNA. This {beta}-domain also regulates RAD54Bs ATPase activity and higher-order oligomer organization on dsDNA. Cellular assays reveal that the NTD RAD51-interacting sites as well as the {beta}-domain are required for repairing camptothecin-induced DSBs by HR in human cells. Our findings uncover a modular architecture and mechanistic framework for RAD54B function in HR, highlighting its critical role in genome maintenance. HighlightsO_LIcryoEM structure of RAD54B in complex with RAD51-DNA complex C_LIO_LIRAD54B uses three sites to interact with RAD51, including a previously unrecognised {beta}-domain that bridges distal RAD51 protomers. C_LIO_LIThe {beta}-domain plays multiple crucial roles including regulating filament stability, RAD54B ATPase activity and RAD54B higher order assembly on DNA. C_LIO_LIRAD54B employs a modular mechanism, with the N-terminal region engaing and stabilising RAD51 filaments, capturing of the homologous strands, whereas the ATPase motor domainrequired for homology search and strand invasion. C_LIO_LIRAD54B N-terminus and {beta}-domain are essential for HR-mediated repair of camptothecin-induced breaks in human cells. C_LI

biochemistry↗
bioRxiv2026

PARP inhibitor synthetic lethality reveals homologous recombination sub-pathway architecture

The DNA damage response (DDR) is a complex network of interconnected pathways and sub-pathways that safeguards genome integrity. Deciphering the coordinated and complementary interactions among these pathways remains a major challenge. In this study, we employed CRISPR screening to systematically map the genetic interactions required for different sub-pathways of homologous recombination in human cells following PARP inhibitor treatment. Our approach recapitulated known interactions and uncovered several previously unrecognized connections. We identified RAD54L, in addition to ATRX, as a factor promoting the double Holliday junction (dHJ) pathway and demonstrated that RAD51AP1 and RAD54B function in synthesis-dependent strand annealing (SDSA). We provide evidence that loss of TOP3A induces a switch in HR sub-pathway usage from SDSA to the dHJ pathway. Furthermore, TOP3A deficiency abolishes the requirement for ATRX and the histone variant H3.3 in the dHJ pathway, while maintaining strict dependence on RAD54L. We further observed that H3.3 is involved in both HR sub-pathways, whereas its depositing chromatin remodelers HIRA and ATRX play pathway-specific roles in SDSA and dHJ, respectively. Together, our findings define the architecture underlying HR sub-pathway choice and reveal a key role for TOP3A in regulating pathway balance.

molecular biology↗