The dynamic pause-unpackaging state, an off-translocation recovery state of a DNA packaging motor from bacteriophage T4

Vishal I. Kottadiel, Venigalla B. Rao, Yann R. Chemla

Research output: Contribution to journalArticle

Abstract

Tailed bacteriophages and herpes viruses use powerful ATP-driven molecular motors to translocate their viral genomes into a preformed capsid shell. The bacteriophage T4 motor, a pentamer of the large terminase protein (gp17) assembled at the portal vertex of the prohead, is the fastest and most powerful known, consistent with the need to package a ∼170-kb viral genome in approximately 5 min. Although much is known about themechanism of DNA translocation, very little is known about how ATP modulates motor-DNA interactions. Here, we report single-molecule measurements of the phage T4 gp17 motor by using dual-trap optical tweezers under different conditions of perturbation. Unexpectedly, themotor pauses randomly when ATP is limiting, for an average of 1 s, and then resumes translocation. During pausing, DNA is unpackaged, a phenomenon so far observed only in T4, where some of the packaged DNA is slowly released. We propose that the motor pauses whenever it encounters a subunit in the apo state with the DNA boundweakly and incorrectly. Pausing allows the subunit to capture ATP, whereas unpackaging allows scanning of DNA until a correct registry is established. Thus, the "pause-unpackaging" state is an off-translocation recovery state wherein the motor, sometimes by taking a few steps backward, can bypass the impediments encountered along the translocation path. These results lead to a four-state mechanochemical model that provides insights into the mechanisms of translocation of an intricately branched concatemeric viral genome.

Original languageEnglish (US)
Pages (from-to)20000-20005
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number49
DOIs
StatePublished - Dec 4 2012

Keywords

  • DNA translocase
  • Optical trap
  • Virus assembly

ASJC Scopus subject areas

  • General

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