1. Department of Physics and Jason L. Choy Laboratory of Single Molecule Biophysics,
2. Biophysics Graduate Group, University of California, Berkeley, California 94720, USA
3. Department of Diagnostic and Biological Sciences,
4. Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA
5. Departments of Molecular and Cell Biology, Chemistry, and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA
6. These authors contributed equally to this work.
7. Present address: Department of Physics and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

Correspondence to: Carlos Bustamante^1,2,5 Correspondence and requests for materials should be addressed to C.B. (Email: carlos@alice.berkeley.edu).

Abstract

Homomeric ring ATPases perform many vital and varied tasks in the cell, ranging from chromosome segregation to protein degradation. Here we report the direct observation of the intersubunit coordination and step size of such a ring ATPase, the double-stranded-DNA packaging motor in the bacteriophage 29. Using high-resolution optical tweezers, we find that packaging occurs in increments of 10 base pairs (bp). Statistical analysis of the preceding dwell times reveals that multiple ATPs bind during each dwell, and application of high force reveals that these 10-bp increments are composed of four 2.5-bp steps. These results indicate that the hydrolysis cycles of the individual subunits are highly coordinated by means of a mechanism novel for ring ATPases. Furthermore, a step size that is a non-integer number of base pairs demands new models for motor–DNA interactions.

1. Department of Physics and Jason L. Choy Laboratory of Single Molecule Biophysics,
2. Biophysics Graduate Group, University of California, Berkeley, California 94720, USA
3. Department of Diagnostic and Biological Sciences,
4. Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA
5. Departments of Molecular and Cell Biology, Chemistry, and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA
6. These authors contributed equally to this work.
7. Present address: Department of Physics and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

Correspondence to: Carlos Bustamante^1,2,5 Correspondence and requests for materials should be addressed to C.B. (Email: carlos@alice.berkeley.edu).

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