Specific tti1 mutation in TTT complex selectively ablates Rad3ATR function in fission yeast

Researchers publishing in PLOS Genetics have used the fission yeast Schizosaccharomyces pombe to probe how a point mutation in Tti1 — a subunit of the Tel2-Tti1-Tti2 (TTT) co-chaperone complex — can specifically eliminate the cellular function of the DNA-damage checkpoint kinase Rad3ATR without disrupting the activity of the other five phosphatidylinositol 3-kinase-related kinases (PIKKs) expressed in that organism.

The TTT complex acts as a co-chaperone during the co-translational maturation of all PIKKs, a family of large kinases with roles in DNA-damage signalling (Rad3ATR and Tel1ATM), nutrient sensing and growth (Tor1 and Tor2, homologues of mammalian mTOR), and transcriptional regulation (Tra1 and Tra2, homologues of TRRAP). Because the complex is required by all six PIKKs, mutations in TTT components have been difficult to study cleanly — loss of the complex typically disrupts multiple pathways simultaneously. The study by Bhadra, Ahamad, Khan, and Xu identifies a tti1 allele that selectively impairs Rad3ATR-dependent signalling, providing a genetic tool to study ATR-pathway biology in isolation.

The authors note that mutations in the TTT complex have recently been linked to human disease syndromes and cancer, making a clearer understanding of how individual TTT mutations translate into specific PIKK-pathway defects potentially relevant to interpreting human variant data. The work is mechanistic model-organism research; findings in S. pombe do not automatically translate to human cells. The study was published in PLOS Genetics on 11 June 2026.