title: Two modes of interaction of the single-stranded DNA-binding protein of bacteriophage T7 with the DNA polymerase-thioredoxin complex.
abstract: The DNA polymerase encoded by bacteriophage T7 has low processivity. Escherichia coli thioredoxin binds to a segment of 76 residues in the thumb subdomain of the polymerase and increases the processivity. The binding of thioredoxin leads to the formation of two basic loops, loops A and B, located within the thioredoxin-binding domain (TBD). Both loops interact with the acidic C terminus of the T7 helicase. A relatively weak electrostatic mode involves the C-terminal tail of the helicase and the TBD, whereas a high affinity interaction that does not involve the C-terminal tail occurs when the polymerase is in a polymerization mode. T7 gene 2.5 single-stranded DNA-binding protein (gp2.5) also has an acidic C-terminal tail. gp2.5 also has two modes of interaction with the polymerase, but both involve the C-terminal tail of gp2.5. An electrostatic interaction requires the basic residues in loops A and B, and gp2.5 binds to both loops with similar affinity as measured by surface plasmon resonance. When the polymerase is in a polymerization mode, the C terminus of gene 2.5 protein interacts with the polymerase in regions outside the TBD. gp2.5 increases the processivity of the polymerase-helicase complex during leading strand synthesis. When loop B of the TBD is altered, abortive DNA products are observed during leading strand synthesis. Loop B appears to play an important role in communication with the helicase and gp2.5, whereas loop A plays a stabilizing role in these interactions.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Sharmistha
authors.initials: S
authors.lastname: Ghosh
authors.forename: Samir M
authors.initials: SM
authors.lastname: Hamdan
authors.forename: Charles C
authors.initials: CC
authors.lastname: Richardson
mesh_terms: D017123:Bacteriophage T7 / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D055672:Static Electricity; D020349:Surface Plasmon Resonance; D013879:Thioredoxins / Q000737:chemistry*
chemical_list: D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D013879:Thioredoxins; D004259:DNA-Directed DNA Polymerase; D008239:Lysine