Abstract

Single stranded DNA (ssDNA) binding proteins (SSBs) bind selectively to ssDNA with high affinity and little sequence specificity, preventing ssDNA from annealing to its complementary sequence. Previously, Ha Lab showed E. coli SSB, a representative homotetrameric SSB, moving on ssDNA however the underlying mechanism for diffusion with such a large binding site size (65 nt of ssDNA) remains unknown. To study the dynamics of SSB diffusion and to study how tension may modulate the motion, a hybrid single-molecule method combining fluorescence and force was used. Experimental evidence was obtained for protein movement along DNA wherein a protein slides via DNA bulge formation. Additionally, force-induced progressive unraveling of ssDNA from the SSB surface between 1 and 6 pN was observed, followed by SSB dissociation at forces greater than 6 pN.

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