ATRIP (ATR-interacting protein) is essential for DNA damage checkpoint signaling and maintaining genomic stability in human cells. ATRIP forms a functional complex with ATR kinase, with the complex adopting a distinctive hollow "heart" shape structure where ATRIP's 14 HEAT repeats in an extended "S" configuration help lock two ATR monomers together 1. The protein is critical for ATR stability and activation, as ATRIP deficiency results in low-grade ATR activation but impaired CHK1 phosphorylation under genotoxic stress 2. ATRIP protects progenitor cells against DNA damage accumulation during DNA replication, and its loss leads to replicative stress and TP53-dependent cell death 3. The protein requires interaction with the MCM replication complex for proper chr3 loading and phosphorylation 4. Clinically, homozygous ATRIP deficiency causes severe developmental abnormalities including microcephalic primordial dwarfism, compromised immunity with lymphopenia, poor vaccine responses, and recurrent infections 2. ATRIP-deficient cells show chr3 instability, compromised cell cycle control, and reduced viability, establishing ATRIP deficiency as a monogenic cause of developmental disorders 2. The ATR-ATRIP complex serves as a target for cancer therapeutics, with several inhibitors currently in clinical trials 5.