Abstract
A new functional interaction of BLM helicase with Rif1, the homolog of a telomere length regulator in yeast, sheds light on one of BLM's less-understood functions, the facilitation of stalled replication fork restart.
BLM, the helicase defective in Bloom syndrome, is part of a multiprotein complex that protects genome stability. Here, we show that Rif1 is a novel component of the BLM complex and works with BLM to promote recovery of stalled replication forks. First, Rif1 physically interacts with the BLM complex through a conserved C-terminal domain, and the stability of Rif1 depends on the presence of the BLM complex. Second, Rif1 and BLM are recruited with similar kinetics to stalled replication forks, and the Rif1 recruitment is delayed in BLM-deficient cells. Third, genetic analyses in vertebrate DT40 cells suggest that BLM and Rif1 work in a common pathway to resist replication stress and promote recovery of stalled forks. Importantly, vertebrate Rif1 contains a DNA-binding domain that resembles the αCTD domain of bacterial RNA polymerase α; and this domain preferentially binds fork and Holliday junction (HJ) DNA
in vitro
and is required for Rif1 to resist replication stress
in vivo
. Our data suggest that Rif1 provides a new DNA-binding interface for the BLM complex to restart stalled replication forks.