Journal
NUCLEIC ACIDS RESEARCH
Volume 44, Issue 3, Pages 1285-1297Publisher
OXFORD UNIV PRESS
DOI: 10.1093/nar/gkv1510
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Funding
- National Science Foundation Award [MCB-1329285]
- National Institutes of Health [R01-GM53158, S10-RR024574]
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [1329285] Funding Source: National Science Foundation
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There is widespread agreement that the clamp loader of the Escherichia coli replicase has the composition DnaX(3)delta delta'chi Psi. Two DnaX proteins exist in E. coli, full length tau and a truncated gamma that is created by ribosomal frameshifting. tau binds DNA polymerase III tightly; gamma does not. There is a controversy as to whether or not DNA polymerase III holoenzyme (Pol III HE) contains gamma. A three-tau form of Pol III HE would contain three Pol IIIs. Proponents of the three-tau hypothesis have claimed that gamma found in Pol III HE might be a proteolysis product of tau. To resolve this controversy, we constructed a strain that expressed only tau from a mutated chromosomal dnaX. gamma containing a C-terminal biotinylation tag (gamma-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 beta) from this strain contained one molecule of gamma-C-tag per Pol III* assembly, indicating that the dominant form of Pol III* in cells is Pol III2 tau(2) delta delta'chi Psi. Revealing a role for lambda in cells, mutants that express only tau 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.
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