The Stability of a Model Substrate for Topoisomerase 1-Mediated DNA Religation Depends on the Presence of Mismatched Base Pairs
Figure 3
Thermal stability of the complex of the 10 mer ssDNA and the 39 mer DNA hairpin constituting a model Top1 religation complex. (a) Melting transition in 10 mM sodium phosphate buffer pH 7; (b) melting transition in the same buffer as A, but with 200 mM NaCl. A biphasic melting profile is observed in both instances. The lower melting temperature corresponds to the dissociation of the ssDNA from the 39 mer DNA hairpin, while the higher melting transition corresponds to the melting temperature for the duplex region of the hairpin. As was observed for the DNA hairpin alone (Figure 2), the melting temperature for the duplex region is sensitive to the presence of a mismatched base pair at the terminus. Surprisingly, the melting temperature for the complex between the single-stranded DNA 10 mer and the single-stranded region of the hairpin is also sensitive to the presence of a base pair mismatch in the duplex region even though the transition does not directly involve the mismatched base pair.
