The bacterial MRE11-RAD50 and DNA2-WRN homologs process replication forks at distinct and separate loci on the...

Human BRCA2 protects the DNA when replication forks stall, whereas MRE11-RAD50 and DNA2-WRN process or partially degrade these substrates. When mutated, these genes result in distinct genetic instabilities and cancers, arguing they have unique, not redundant, functions. Escherichia coli encodes functional homologs of MRE11-RAD50 (SbcC-SbcD), DNA2-WRN (RecJ-RecQ), and BRCA2 (RecF). Here, we use 2-dimensional gels, pulse-labelling, and replication-profiling analysis to show the bacterial homologs act at distinct substrates and loci on the chromosome. Whereas RecF and RecJ-RecQ protect and process DNA at arrested replication forks to facilitate repair, RecBCD and SbcC-SbcD protect and process DNA at sites where forks converge. Comparing the assays used in E. coli to human cells, we consider whether these cellular roles may be functionally conserved. Impact statement BRCA2, MRE11-RAD50, and WRN-DNA2 encode human proteins that process replication forks and result in distinct genetic instabilities and cancers when mutated. Here, we show their bacterial homologs act on unique replication fork substrates-those at DNA damage sites or as replication completes, and discuss their possible functional conservation in humans.