DNA polymerase actively and sequentially displaces single-stranded DNA-binding proteins

Xu, L.F.; Jin, S.K.; Urem, M.; Lee, S.J.; Lamers, M.H.; Chen, X.; Wolynes, P.G.; Wuite, G.J.L.

doi:doi:10.1038/s41467-025-62531-1

Single-stranded DNA-binding proteins (SSBs) protect transiently exposed ssDNA, yet how DNA polymerase (DNAp) displaces them during replication remains unclear. Using single-molecule force spectroscopy, dual-color imaging, and molecular dynamics simulations on bacteriophage T7 DNAp and SSB, we investigated molecular mechanisms underlying SSB displacement. T7 SSB modulates replication in a force-dependent manner: enhancing it at low tension by preventing secondary structures while impeding it at high tension. Dual-color imaging shows SSBs remain stationary as DNAp advances, supporting a sequential displacement model. Molecular dynamics suggests that DNAp actively lowers the SSB dissociation energy barrier through interactions mediated by the SSB C-terminal tail. FRET confirms close protein proximity during encounters. Optimal replication requires SSB saturation of ssDNA, establishing a delicate balance between protection and efficiency. This spatiotemporal coordination between DNAp...Show moreSingle-stranded DNA-binding proteins (SSBs) protect transiently exposed ssDNA, yet how DNA polymerase (DNAp) displaces them during replication remains unclear. Using single-molecule force spectroscopy, dual-color imaging, and molecular dynamics simulations on bacteriophage T7 DNAp and SSB, we investigated molecular mechanisms underlying SSB displacement. T7 SSB modulates replication in a force-dependent manner: enhancing it at low tension by preventing secondary structures while impeding it at high tension. Dual-color imaging shows SSBs remain stationary as DNAp advances, supporting a sequential displacement model. Molecular dynamics suggests that DNAp actively lowers the SSB dissociation energy barrier through interactions mediated by the SSB C-terminal tail. FRET confirms close protein proximity during encounters. Optimal replication requires SSB saturation of ssDNA, establishing a delicate balance between protection and efficiency. This spatiotemporal coordination between DNAp and SSB is critical for resolving molecular collisions and may represent a general mechanism for resolving molecular collisions, ensuring both processivity and genomic integrity.Show less

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DNA polymerase actively and sequentially displaces single-stranded DNA-binding proteins