A stalled fork stalls recombination

Homologous recombination does not rescue stalled replication forks during S phase, report Meister et al. on page 537. Rather they find that replication and recombination are separated in terms of when and where they occur. If inappropriate recombination does occur when replication is stalled, replication forks fall apart.Researchers have debated whether homologous recombination, which is required for double-strand break repair, is also used to resolve stalled replication forks. However, because the S- and G2/M-phase checkpoints share molecular components in budding yeast, the question has been difficult to answer.

Now, Meister et al. test the question in fission yeast, where the checkpoints are molecularly distinct and therefore can be separated. When they added hydroxyurea to wild-type cells, thus depleting DNA precursors and stalling replication, the recombination protein...