DONSON and FANCM associate with different replisomes distinguished by replication timing and chromatin domain

Abstract

Duplication of mammalian genomes requires replisomes to overcome numerous impediments during passage through open (eu) and condensed (hetero) chromatin. Typically, studies of replication stress characterize mixed populations of challenged and unchallenged replication forks, averaged across S phase, and model a single species of "stressed" replisome. Here, in cells containing potent obstacles to replication, we find two different lesion proximal replisomes. One is bound by the DONSON protein and is more frequent in early S phase, in regions marked by euchromatin. The other interacts with the FANCM DNA translocase, is more prominent in late S phase, and favors heterochromatin. The two forms can also be detected in unstressed cells. ChIP-seq of DNA associated with DONSON or FANCM confirms the bias of the former towards regions that replicate early and the skew of the latter towards regions that replicate late.

Replication Stress, Genomic Instability, and Replication Timing: A Complex Relationship

“…ORC was observed to preferentially bind to early-replicating chromatin regions and transcription start sites of actively transcribed genes [ 99 ]. Furthermore, the proteins DONSON and FANCM are associated with euchromatin replicated early in the S-phase and heterochromatin replicated in the late S-phase, respectively [ 100 ]. All of these studies suggest that DNA–protein interactions have a direct role in the establishment of RT that may be modified and/or reinforced in response to replication stress; however, this has not been fully demonstrated to date.…”

Replication of the Mammalian Genome by Replisomes Specific for Euchromatin and Heterochromatin

“…These results were consistent with DONSON being retained on replisomes transiently proximal to ICLs, unlike the GINS proteins. Furthermore, following ATR inhibition there was an accumulation of DONSON containing replisomes stalled at ICLs ( Zhang et al, 2020 ).…”

“…Thus, there were separate and distinguishable stressed replisomes containing either DONSON or FANCM but not both. Furthermore, DONSON clearly had a different role than FANCM because it was associated with both stressed and unstressed replisomes while FANCM was associated only with stressed replisomes ( Zhang et al, 2020 ). This argued against the assumption of a single species of stressed replisome and raised the question: Do these different replisome complexes exist in the same cell at the same time?…”

Downstream Neighbor of SON (DONSON) Expression Is Enhanced in Phenotypically Aggressive Prostate Cancers

“…Nevertheless, due to its function in DNA replication and repair, an additional nuclear expression would have been expected. During the S phase, nuclear DONSON foci were observed [ 9 ]. However, the DNA replication and S phase only describes a small part of the cell cycle, and thus the localization of DONSON could differ during the G1 phase [ 24 ].…”

“…Thus, DONSON was found to be a robust biomarker for risk stratification in clear cell renal cell carcinoma (ccRCC), and in vitro, DONSON was linked to a malignant phenotype in ccRCC cell culture models [ 7 , 8 ]. Mechanistically, it is known that DONSON represents a critical replication fork protein required for physiological DNA replication [ 9 ]. DONSON is pivotal for genome stability and integrity as severe replication-associated DNA damage was observed after depletion of DONSON [ 10 ].…”