Cryo-EM structure of the human CST-Polα/primase complex in a recruitment state

The CST-Pol alpha/primase complex is essential for telomere maintenance and functions to counteract resection at double-strand breaks. We report a 4.6-angstrom resolution cryo-EM structure of human CST-Pol alpha/primase, captured prior to catalysis in a recruitment state stabilized by chemical cross-linking. Our structure reveals an evolutionarily conserved interaction between the C-terminal domain of the catalytic POLA1 subunit and an N-terminal expansion in metazoan CTC1. Cross-linking mass spectrometry and negative-stain EM analysis provide insight into CST binding by the flexible POLA1 N-terminus. Finally, Coats plus syndrome disease mutations previously characterized to disrupt formation of the CST-Pol alpha/primase complex map to protein-protein interfaces observed in the recruitment state. Together, our results shed light on the architecture and stoichiometry of the metazoan fill-in machinery.

Automated summary

This study reports a cryo-EM structure of human CST-Pol alpha/primase and reveals an evolutionarily conserved interaction between POLA1 and CTC1. The binding mode of CST to the N-terminus of POLA1 is revealed by negative-stain EM and cross-linking mass spectrometry. In addition, disease mutations associated with Coats plus syndrome disrupt protein-protein interfaces observed in the recruitment state.