Biology subjects

Bosire, R.

Publications and source records attributed to Bosire, R..

3 recordsLinked to original sources

bioRxiv2025

The BRCA1- RAD51 Axis Regulates SCAI/REV3 Dependent Replication Fork Maintenance

Replication stress is a key contributor to genomic instability and cancers. BRCA1 has well established roles in protecting stalled forks against degradation. Here we show that BRCA1 has a fork protection-independent role via regulation of RAD51 in a manner that confers dependency on SCAI and REV3. SCAI loss leads to elevated DNA breaks, genomic instability and cell death upon DNA damage. We show that the increased DNA breaks occur in S phase, consistent with fork breakage. BRCA1 drives SLX4-SLX1-ERCC1 mediated DNA break formation in the absence of SCAI and REV3, which are required to maintain integrity of stalled forks for efficient restart. Domain analysis revealed that the increased break signaling seen in the absence of SCAI does not require binding to resection factors like CtIP. Surprisingly, loss of fork reversal factors leads to additive increases in damage signaling and elevated fork shortening in the absence of SCAI/REV3 in a manner that depends on RAD51 activity. We propose that Protexin may be required to replicate through and maintain stalled replication forks at fragile genomic regions. Failure to do so leads to increased DNA breakage and genomic instability.

cell biology↗

bioRxiv2023

RADIF(C1orf112)-FIGNL1 Complex Regulates RAD51 Chromatin Association to Promote Viability After Replication Stress

Homologous recombination (HR) plays critical roles in repairing lesions that arise during DNA replication and is thus essential for viability. RAD51 plays important roles during replication and HR, however, how RAD51 is regulated downstream of nucleofilament formation and how the varied RAD51 functions are regulated is not clear. We have investigated the poorly characterized protein c1orf112/RADIF that previously scored in genome-wide screens for mediators of DNA inter-strand crosslink (ICL) repair. Upon ICL agent exposure, RADIF loss leads to marked cell death, elevated chromosomal instability, increased micronuclei formation, altered cell cycle progression and increased DNA damage signaling. RADIF is recruited to damage foci and forms a complex with FIGNL1. Both proteins have epistatic roles in ICL repair, forming a co-stable complex. Mechanistically, RADIF loss leads to increased RAD51 amounts and foci on chromatin both with or without exogenous DNA damage, defective replication fork progression and reduced HR competency. We posit that RADIF is essential for limiting RAD51 levels on chromatin in the absence of damage and for RAD51 dissociation from nucleofilaments to properly complete HR. Failure to do so leads to replication slowing and inability to complete repair.

biochemistry↗

bioRxiv2021

Fundamental Role Of The H2A.Z C-Terminal Tail In The Formation Of Constitutive Heterochromatin

H2A.Z-nucleosomes are present in both euchromatin and heterochromatin and it has proven difficult to interpret their disparate roles in the context of their stability features. Using an in situ assay of nucleosome stability and DT40 cells expressing engineered forms of the histone variant we show that native H2A.Z, but not C-terminally truncated H2A.Z (H2A.Z{Delta}C), is released from nucleosomes of peripheral heterochromatin at unusually high salt concentrations. H2A.Z and H3K9me3 landscapes are reorganized in H2A.Z{Delta}C-nuclei and overall sensitivity of chromatin to nucleases is increased. These tail-dependent differences are recapitulated upon treatment of HeLa nuclei with the H2A.Z-tail-peptide (C9), with MNase sensitivity being increased at specific regions including promoters. Introduced into live cells C9 elicits down-regulation of [~]560 genes with nonrandom chromosomal band-localization and pathway-spectrum. Thus, tail-dependent heterogeneity of H2A.Z-nucleosomes is revealed at all organization levels of chromatin and epigenetic modulation can be achieved by targeting molecular interactions involving its C-terminal tail.

cell biology↗