Interactions of Escherichia coli thioredoxin, the processivity factor, with bacteriophage T7 DNA polymerase and helicase

Sharmistha Ghosh, Samir M. Hamdan, Timothy E. Cook, Charles C. Richardson

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Escherichia coli thioredoxin binds to a unique flexible loop of 71 amino acid residues, designated the thioredoxin binding domain (TBD), located in the thumb subdomain of bacteriophage T7 gene 5 DNA polymerase. The initial designation of thioredoxin as a processivity factor was premature. Rather it remodels the TBD for interaction with DNA and the other replication proteins. The binding of thioredoxin exposes a number of basic residues on the TBD that lie over the duplex region of the primer-template and increases the processivity of nucleotide polymerization. Two small solvent-exposed loops (loops A and B) located within TBD electrostatically interact with the acidic C-terminal tail of T7 gene 4 helicase-primase, an interaction that is enhanced by the binding of thioredoxin. Several basic residues on the surface of thioredoxin in the polymerase-thioredoxin complex lie in close proximity to the TBD. One of these residues, lysine 36, is located proximal to loop A. The substitution of glutamate for lysine has a dramatic effect on the binding of gene 4 helicase to a DNA polymerase-thioredoxin complex lacking charges on loop B; binding is decreased 15-fold relative to that observed with wild-type thioredoxin. This defective interaction impairs the ability of T7DNApolymerase-thioredoxin together with T7 helicase to mediate strand displacement synthesis. This is the first demonstration that thioredoxin interacts with replication proteins other than T7 DNA polymerase.

Original languageEnglish (US)
Pages (from-to)32077-32084
Number of pages8
JournalJournal of Biological Chemistry
Issue number46
StatePublished - Nov 14 2008
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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