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The DNA polymerase III holoenzyme contains ? and is not a trimeric polymerase.

ABSTRACT: There is widespread agreement that the clamp loader of the Escherichia coli replicase has the composition DnaX3??'??. Two DnaX proteins exist in E. coli, full length ? and a truncated ? that is created by ribosomal frameshifting. ? binds DNA polymerase III tightly; ? does not. There is a controversy as to whether or not DNA polymerase III holoenzyme (Pol III HE) contains ?. A three-? form of Pol III HE would contain three Pol IIIs. Proponents of the three-? hypothesis have claimed that ? found in Pol III HE might be a proteolysis product of ?. To resolve this controversy, we constructed a strain that expressed only ? from a mutated chromosomal dnaX. ? containing a C-terminal biotinylation tag (?-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 ?) from this strain contained one molecule of ?-C(tag) per Pol III* assembly, indicating that the dominant form of Pol III* in cells is Pol III2?2 ???'??. Revealing a role for ? in cells, mutants that express only ? 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.

SUBMITTER: Dohrmann PR 

PROVIDER: S-EPMC4756838 | biostudies-other | 2016 Feb

REPOSITORIES: biostudies-other

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The DNA polymerase III holoenzyme contains γ and is not a trimeric polymerase.

Dohrmann Paul R PR   Correa Raul R   Frisch Ryan L RL   Rosenberg Susan M SM   McHenry Charles S CS  

Nucleic acids research 20160118 3

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 i  ...[more]

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