RTEL1 in DNA Replication Genome stability requires the coordinate action of a variety of DNA maintenance systems. The DNA helicase, RTEL1 (regulator of telomere length 1), disassembles recombination intermediates to avoid dangerous by-products. RTEL1 also limits excessive meiotic crossing over and disassembles telomere T loops. Vannier et al. (p. 239 ) now show that mammalian RTEL1 is part of the DNA replication machinery. RTEL1 binds to proliferating cell nuclear antigen (PCNA), an interaction that was important for normal DNA replication, replication fork stability, and telomere stability. The RTEL1-PCNA interaction was also critical for protecting cells against tumorigenesis but was not required for telomere T-loop disassembly.