The DNA polymerase III holoenzyme contains γ and is not a trimeric polymerase.
نویسندگان
چکیده
There is widespread agreement that the clamp loader of the Escherichia coli replicase has the composition DnaX3δδ'χψ. Two DnaX proteins exist in E. coli, full length τ and a truncated γ that is created by ribosomal frameshifting. τ binds DNA polymerase III tightly; γ does not. There is a controversy as to whether or not DNA polymerase III holoenzyme (Pol III HE) contains γ. A three-τ form of Pol III HE would contain three Pol IIIs. Proponents of the three-τ hypothesis have claimed that γ found in Pol III HE might be a proteolysis product of τ. To resolve this controversy, we constructed a strain that expressed only τ from a mutated chromosomal dnaX. γ containing a C-terminal biotinylation tag (γ-C(tag)) was provided in trans at physiological levels from a plasmid. A 2000-fold purification of Pol III* (all Pol III HE subunits except β) from this strain contained one molecule of γ-C(tag) per Pol III* assembly, indicating that the dominant form of Pol III* in cells is Pol III2τ2 γδδ'χψ. Revealing a role for γ in cells, mutants that express only τ display sensitivity to ultraviolet light and reduction in DNA Pol IV-dependent mutagenesis associated with double-strand-break repair, and impaired maintenance of an F' episome.
منابع مشابه
Characterization of a triple DNA polymerase replisome.
The replicase of all cells is thought to utilize two DNA polymerases for coordinated synthesis of leading and lagging strands. The DNA polymerases are held to DNA by circular sliding clamps. We demonstrate here that the E. coli DNA polymerase III holoenzyme assembles into a particle that contains three DNA polymerases. The three polymerases appear capable of simultaneous activity. Furthermore, ...
متن کاملDNA Polymerase III of Escherichia coli
DNA polymerase III, the core of the DNA polymerase III holoenzyme, has been purified Z&000-fold to 97% homogeneity from Escherichiu coli HMS-83. The enzyme contains three subunits: (Y, E, and 0 of 140,000, 25,000, and 10,000 daltons, respectively. The cy subunit has been previously shown to be a component of both DNA polymerase III and the more complex DNA polymerase III holoenzyme (Livingston,...
متن کاملDNA Polymerase III of Escherichia coli
DNA polymerase III, the core of the DNA polymerase III holoenzyme, has been purified Z&000-fold to 97% homogeneity from Escherichiu coli HMS-83. The enzyme contains three subunits: (Y, E, and 0 of 140,000, 25,000, and 10,000 daltons, respectively. The cy subunit has been previously shown to be a component of both DNA polymerase III and the more complex DNA polymerase III holoenzyme (Livingston,...
متن کاملDNA Polymerase III of Escherichia coli
DNA polymerase III, the core of the DNA polymerase III holoenzyme, has been purified Z&000-fold to 97% homogeneity from Escherichiu coli HMS-83. The enzyme contains three subunits: (Y, E, and 0 of 140,000, 25,000, and 10,000 daltons, respectively. The cy subunit has been previously shown to be a component of both DNA polymerase III and the more complex DNA polymerase III holoenzyme (Livingston,...
متن کاملDNA Polymerase III of Escherichia coli
DNA polymerase III, the core of the DNA polymerase III holoenzyme, has been purified Z&000-fold to 97% homogeneity from Escherichiu coli HMS-83. The enzyme contains three subunits: (Y, E, and 0 of 140,000, 25,000, and 10,000 daltons, respectively. The cy subunit has been previously shown to be a component of both DNA polymerase III and the more complex DNA polymerase III holoenzyme (Livingston,...
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عنوان ژورنال:
- Nucleic acids research
دوره 44 3 شماره
صفحات -
تاریخ انتشار 2016