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. 1997 Apr 1;94(7):2987–2992. doi: 10.1073/pnas.94.7.2987

Figure 1.

Figure 1

Scheme for T7 gene 4 helicase-mediated strand transfer. A joint molecule consisting of circular, single-stranded M13 DNA annealed to a 3′-single-stranded terminus of homologous linear, double-stranded M13 DNA. The hexameric T7 gene 4 helicase binds to the 5′-displaced single-stranded terminus created by spontaneous branch migration and translocates in a 5′-to-3′ direction to unwind the duplex DNA at the expense of the hydrolysis of a NTP. As the unwinding proceeds the newly exposed single-stranded DNA (ssDNA) on the duplex partner base pairs to the complementary region on the ssDNA circle. The continuous polar strand transfer results in the formation of a circular, double-stranded DNA (dsDNA) molecule and a linear, ssDNA molecule.