DNA synthesis provides the driving force to accelerate DNA unwinding by a helicase


Helicases are molecular motors that use the energy of nucleoside 5′-triphosphate (NTP) hydrolysis to translocate along a nucleic acid strand and catalyse reactions such as DNA unwinding. The ring-shaped helicase1 of bacteriophage T7 translocates along single-stranded (ss)DNA at a speed of 130 bases per second2; however, T7 helicase slows down nearly tenfold when unwinding the strands of duplex DNA3. Here, we report that T7 DNA polymerase, which is unable to catalyse strand displacement DNA synthesis by itself, can increase the unwinding rate to 114 base pairs per second, bringing the helicase up to similar speeds compared to its translocation along ssDNA. The helicase rate of stimulation depends upon the DNA synthesis rate and does not rely on specific interactions between T7 DNA polymerase and the carboxy-terminal residues of T7 helicase. Efficient duplex DNA synthesis is achieved only by the combined action of the helicase and polymerase. The strand displacement DNA synthesis by the DNA polymerase depends on the unwinding activity of the helicase, which provides ssDNA template. The rapid trapping of the ssDNA bases by the DNA synthesis activity of the polymerase in turn drives the helicase to move forward through duplex DNA at speeds similar to those observed along ssDNA.

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Figure 1: DNA synthesis by T7 DNA polymerase.
Figure 2: The unwinding rate of T7 helicase depends on the speed of DNA synthesis.
Figure 3: DNA synthesis by T7 DNA polymerase and T7 helicase.
Figure 4: DNA synthesis by T4 and T7 DNA polymerases and T7 helicase.


  1. 1

    Patel, S. S. & Picha, K. M. Structure and function of hexameric helicases. Annu. Rev. Biochem. 69, 651–697 (2000)

    CAS  Article  Google Scholar 

  2. 2

    Kim, D. E., Narayan, M. & Patel, S. S. T7 DNA helicase: a molecular motor that processively and unidirectionally translocates along single-stranded DNA. J. Mol. Biol. 321, 807–819 (2002)

    CAS  Article  Google Scholar 

  3. 3

    Jeong, Y. J., Levin, M. K. & Patel, S. S. The DNA-unwinding mechanism of the ring helicase of bacteriophage T7. Proc. Natl Acad. Sci. USA 101, 7264–7269 (2004)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Richardson, C. C. Bacteriophage T7: minimal requirements for the replication of a duplex DNA molecule. Cell 33, 315–317 (1983)

    CAS  Article  Google Scholar 

  5. 5

    Lee, J., Chastain, P. D., Kusakabe, T., Griffith, J. D. & Richardson, C. C. Coordinated leading and lagging strand DNA synthesis on a minicircular template. Mol. Cell 1, 1001–1010 (1998)

    CAS  Article  Google Scholar 

  6. 6

    Patel, S. S., Wong, I. & Johnson, K. A. Pre-steady-state kinetic analysis of processive DNA replication including complete characterization of an exonuclease-deficient mutant. Biochemistry 30, 511–525 (1991)

    CAS  Article  Google Scholar 

  7. 7

    Matson, S. W. & Richardson, C. C. DNA-dependent nucleoside 5′-triphosphatase activity of the gene 4 protein of bacteriophage T7. J. Biol. Chem. 258, 14009–14016 (1983)

    CAS  PubMed  Google Scholar 

  8. 8

    Matson, S. W., Tabor, S. & Richardson, C. C. The gene 4 protein of bacteriophage T7. Characterization of helicase activity. J. Biol. Chem. 258, 14017–14024 (1983)

    CAS  PubMed  Google Scholar 

  9. 9

    Patel, S. S., Rosenberg, A. H., Studier, F. W. & Johnson, K. A. Large scale purification and biochemical characterization of T7 primase/helicase proteins. Evidence for homodimer and heterodimer formation. J. Biol. Chem. 267, 15013–15021 (1992)

    CAS  PubMed  Google Scholar 

  10. 10

    Ali, J. A. & Lohman, T. M. Kinetic measurement of the step size of DNA unwinding by Escherichia coli UvrD helicase. Science 275, 377–380 (1997)

    CAS  Article  Google Scholar 

  11. 11

    Notarnicola, S. M., Mulcahy, H. L., Lee, J. & Richardson, C. C. The acidic carboxyl terminus of the bacteriophage T7 gene 4 helicase/primase interacts with T7 DNA polymerase. J. Biol. Chem. 272, 18425–18433 (1997)

    CAS  Article  Google Scholar 

  12. 12

    von Hippel, P. H. & Delagoutte, E. A general model for nucleic acid helicases and their “coupling” within macromolecular machines. Cell 104, 177–190 (2001)

    CAS  Article  Google Scholar 

  13. 13

    Kim, Y. T., Tabor, S., Bortner, C., Griffith, J. D. & Richardson, C. C. Purification and characterization of the bacteriophage T7 gene 2.5 protein. A single-stranded DNA-binding protein. J. Biol. Chem. 267, 15022–15031 (1992)

    CAS  PubMed  Google Scholar 

  14. 14

    Lohman, T. M. & Ferrari, M. E. Escherichia coli single-stranded DNA-binding protein: multiple DNA-binding modes and cooperativities. Annu. Rev. Biochem. 63, 527–570 (1994)

    CAS  Article  Google Scholar 

  15. 15

    Delagoutte, E. & von Hippel, P. H. Molecular mechanisms of the functional coupling of the helicase (gp41) and polymerase (gp43) of bacteriophage T4 within the DNA replication fork. Biochemistry 40, 4459–4477 (2001)

    CAS  Article  Google Scholar 

  16. 16

    Levin, M. K. & Patel, S. S. in Molecular Motors (ed. Schliwa, M.) 179–198 (Wiley, Weinheim, 2003)

    Google Scholar 

  17. 17

    Levin, M. K., Gurjar, M. M. & Patel, S. S. ATP binding modulates the nucleic acid affinity of hepatitis C virus helicase. J. Biol. Chem. 278, 23311–23316 (2003)

    CAS  Article  Google Scholar 

  18. 18

    Wang, H. & Oster, G. Ratchets, power strokes, and molecular motors. Applied Phys. A 75, 315–323 (2002)

    ADS  CAS  Article  Google Scholar 

  19. 19

    Kim, S., Dallmann, H. G., McHenry, C. S. & Marians, K. J. Coupling of a replicative polymerase and helicase: a tau-DnaB interaction mediates rapid replication fork movement. Cell 84, 643–650 (1996)

    CAS  Article  Google Scholar 

  20. 20

    Mok, M. & Marians, K. J. The Escherichia coli preprimosome and DNA B helicase can form replication forks that move at the same rate. J. Biol. Chem. 262, 16644–16654 (1987)

    CAS  PubMed  Google Scholar 

  21. 21

    Korhonen, J. A., Pham, X. H., Pellegrini, M. & Falkenberg, M. Reconstitution of a minimal mtDNA replisome in vitro. EMBO J. 23, 2423–2429 (2004)

    CAS  Article  Google Scholar 

  22. 22

    Schrock, R. D. & Alberts, B. Processivity of the gene 41 DNA helicase at the bacteriophage T4 DNA replication fork. J. Biol. Chem. 271, 16678–16682 (1996)

    CAS  Article  Google Scholar 

  23. 23

    Cha, T. A. & Alberts, B. M. The bacteriophage T4 DNA replication fork. Only DNA helicase is required for leading strand DNA synthesis by the DNA polymerase holoenzyme. J. Biol. Chem. 264, 12220–12225 (1989)

    CAS  PubMed  Google Scholar 

  24. 24

    Frey, M. W., Nossal, N. G., Capson, T. L. & Benkovic, S. J. Construction and characterization of a bacteriophage T4 DNA polymerase deficient in 3′ → 5′ exonuclease activity. Proc. Natl Acad. Sci. USA 90, 2579–2583 (1993)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Lucius, A. L., Maluf, N. K., Fischer, C. J. & Lohman, T. M. General methods for analysis of sequential “n-step” kinetic mechanisms: Application to single turnover kinetics of helicase-catalyzed DNA unwinding. Biophys. J. 85, 2224–2239 (2003)

    CAS  Article  Google Scholar 

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We thank M. O'Donnell, A. Berdis, N. Andraos, C. C. Richardson and M. Salas for the gift of proteins, and C. M. Drain for critical reading of the manuscript. This research was supported by an NIH grant to S.S.P.

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Correspondence to Smita S. Patel.

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Supplementary information

Supplementary Figure 1

The effect of ssDNA-binding proteins on the unwinding activity of T7 helicase. (JPG 19 kb)

Supplementary Legend

This file contains the legend for Supplementary Fig. 1. (DOC 21 kb)

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Stano, N., Jeong, Y., Donmez, I. et al. DNA synthesis provides the driving force to accelerate DNA unwinding by a helicase. Nature 435, 370–373 (2005). https://doi.org/10.1038/nature03615

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