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Gene Review

dnaX  -  DNA polymerase III/DNA elongation factor...

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK0464, JW0459, dnaZ
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Disease relevance of dnaX

  • The dnaX gene (previously called dnaZX) of Escherichia coli has only one open reading frame for a 71-kDa polypeptide from which two distinct DNA polymerase III holoenzyme subunits, tau (71 kDa) and gamma (47 kDa), are produced [1].
  • Thermus thermophilis dnaX homolog encoding gamma- and tau-like proteins of the chromosomal replicase [2].
  • A 0.2 kb fragment of DNA located immediately upstream of the Caulobacter homolog of the Escherichia coli dnaX gene was able to completely rescue the temperature-sensitive phenotype of LS439 [3].
  • To help evaluate the role of the dispensable gamma, the distribution of tau and gamma homologs in several other species and the sequence of the Salmonella typhimurium dnaX were determined [4].
  • The Bacillus subtilis small cytoplasmic RNA gene and 'dnaX' map near the chromosomal replication origin [5].

High impact information on dnaX

  • Sequence requirements for efficient translational frameshifting in the Escherichia coli dnaX gene and the role of an unstable interaction between tRNA(Lys) and an AAG lysine codon [6].
  • We isolated a mutant allele of dnaX, encoding the tau and gamma subunits of the DNA polymerase III holoenzyme, that causes extreme cell filamentation but does not affect either cell growth or DNA replication [7].
  • Third, transformation of mutD5 strains with multicopy plasmids expressing the mutH or mutL gene restores mismatch repair, even in rapidly growing cells [8].
  • In E. coli, approximately 50% of initiating ribosomes translate the dnaX mRNA conventionally to give tau, but the other 50% shift into the -1 reading frame at a specific site (A AAA AAG) in the mRNA to produce gamma [9].
  • Heteroduplexes in defined states of methylation at d(GATC) sites were used to transform a repair-proficient indicator strain (which has a mnt-lac fusion coding for a nonfunctional mnt repressor) and its isogenic mutH, -L, and -S derivatives [10].

Chemical compound and disease context of dnaX


Biological context of dnaX

  • In this report, we describe the use of dnaX-lacZ fusions in all three reading frames to demonstrate that gamma, the shorter product of dnaX, is generated by ribosomal frameshifting to the -1 reading frame of the mRNA within an oligo(A) sequence that is followed by a sequence predicted to form a stable secondary structure [12].
  • The dnaZ and dnaX loci of Escherichia coli have been genetically defined as separate genes, both of which are essential for DNA replication (1) [13].
  • A search for new mutators in the dnaX region of the chromosome yielded six additional dnaX mutators, all carrying a specific tau subunit defect [14].
  • In cells carrying this plasmid, the activity that complements a mutant dnaZ extract in replicating a primed single-stranded DNA circle was increased about 20-fold [15].
  • The N-terminal amino acid sequences of the first 12 residues were identical in both subunits, as were their molar specific activities in dnaZ complementation [15].

Associations of dnaX with chemical compounds

  • Moreover, the stage I synthesis of G13 DNA in dnaZ was thermosensitive in nutrient broth but not in Tris/casamino acids/glucose medium [16].
  • We demonstrate further that this repair activity results from MMR recognition of base pairs containing 8-oxoguanine (8-oxoG) based on the finding that overexpression of the MutM oxidative repair protein, which repairs 8-oxoG, can suppress the mutH-dependent increase in transversion mutations [17].
  • Early intermediate DNA synthesized in a dnaZ extract can be converted to fully replicated plasmid molecules upon addition to a replication enzyme fraction prepared by ammonium sulfate fractionation of polA I extracts [18].

Other interactions of dnaX


Analytical, diagnostic and therapeutic context of dnaX


  1. Translational frameshifting generates the gamma subunit of DNA polymerase III holoenzyme. Tsuchihashi, Z., Kornberg, A. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  2. Thermus thermophilis dnaX homolog encoding gamma- and tau-like proteins of the chromosomal replicase. Yurieva, O., Skangalis, M., Kuriyan, J., O'Donnell, M. J. Biol. Chem. (1997) [Pubmed]
  3. Use of flow cytometry to identify a Caulobacter 4.5 S RNA temperature-sensitive mutant defective in the cell cycle. Winzeler, E., Shapiro, L. J. Mol. Biol. (1995) [Pubmed]
  4. Conservation of the Escherichia coli dnaX programmed ribosomal frameshift signal in Salmonella typhimurium. Blinkova, A., Burkart, M.F., Owens, T.D., Walker, J.R. J. Bacteriol. (1997) [Pubmed]
  5. The Bacillus subtilis small cytoplasmic RNA gene and 'dnaX' map near the chromosomal replication origin. Struck, J.C., Alonso, J.C., Toschka, H.Y., Erdmann, V.A. Mol. Gen. Genet. (1990) [Pubmed]
  6. Sequence requirements for efficient translational frameshifting in the Escherichia coli dnaX gene and the role of an unstable interaction between tRNA(Lys) and an AAG lysine codon. Tsuchihashi, Z., Brown, P.O. Genes Dev. (1992) [Pubmed]
  7. Temporal regulation of topoisomerase IV activity in E. coli. Espeli, O., Levine, C., Hassing, H., Marians, K.J. Mol. Cell (2003) [Pubmed]
  8. The extreme mutator effect of Escherichia coli mutD5 results from saturation of mismatch repair by excessive DNA replication errors. Schaaper, R.M., Radman, M. EMBO J. (1989) [Pubmed]
  9. Nonlinearity in genetic decoding: homologous DNA replicase genes use alternatives of transcriptional slippage or translational frameshifting. Larsen, B., Wills, N.M., Nelson, C., Atkins, J.F., Gesteland, R.F. Proc. Natl. Acad. Sci. U.S.A. (2000) [Pubmed]
  10. Repair of DNA heteroduplexes containing small heterologous sequences in Escherichia coli. Parker, B.O., Marinus, M.G. Proc. Natl. Acad. Sci. U.S.A. (1992) [Pubmed]
  11. Mapping of two transcription mutations (tlnI and tlnII) conferring thiolutin resistance, adjacent to dnaZ and rho in Escherichia coli. Sivasubramanian, N., Jayaraman, R. Mol. Gen. Genet. (1980) [Pubmed]
  12. The gamma subunit of DNA polymerase III holoenzyme of Escherichia coli is produced by ribosomal frameshifting. Flower, A.M., McHenry, C.S. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  13. The adjacent dnaZ and dnaX genes of Escherichia coli are contained within one continuous open reading frame. Flower, A.M., McHenry, C.S. Nucleic Acids Res. (1986) [Pubmed]
  14. Mutator mutants of Escherichia coli carrying a defect in the DNA polymerase III tau subunit. Pham, P.T., Zhao, W., Schaaper, R.M. Mol. Microbiol. (2006) [Pubmed]
  15. DNA polymerase III holoenzyme of Escherichia coli. I. Purification and distinctive functions of subunits tau and gamma, the dnaZX gene products. Maki, S., Kornberg, A. J. Biol. Chem. (1988) [Pubmed]
  16. Replication of bacteriophage G13 DNA in dna mutants of Escherichia coli. Taketo, A., Kodaira, K. Biochim. Biophys. Acta (1978) [Pubmed]
  17. The Escherichia coli methyl-directed mismatch repair system repairs base pairs containing oxidative lesions. Wyrzykowski, J., Volkert, M.R. J. Bacteriol. (2003) [Pubmed]
  18. Replication of the ampicillin resistance plasmid RSF1030 in extracts of Escherichia coli: separation of the replication cycle into early and late stages. Staudenbauer, W.L. Mol. Gen. Genet. (1977) [Pubmed]
  19. Eukaryotic Mr 83,000 heat shock protein has a homologue in Escherichia coli. Bardwell, J.C., Craig, E.A. Proc. Natl. Acad. Sci. U.S.A. (1987) [Pubmed]
  20. DNA polymerase III holoenzyme of Escherichia coli: components and function of a true replicative complex. McHenry, C.S. Mol. Cell. Biochem. (1985) [Pubmed]
  21. Interaction of the Escherichia coli dnaA initiation protein with the dnaZ polymerization protein in vivo. Walker, J.R., Ramsey, J.A., Haldenwang, W.G. Proc. Natl. Acad. Sci. U.S.A. (1982) [Pubmed]
  22. Identification, isolation, and characterization of the structural gene encoding the delta' subunit of Escherichia coli DNA polymerase III holoenzyme. Carter, J.R., Franden, M.A., Aebersold, R., McHenry, C.S. J. Bacteriol. (1993) [Pubmed]
  23. Monoclonal antibodies specific for the tau subunit of the DNA polymerase III holoenzyme of Escherichia coli. Use to demonstrate that tau is the product of the dnaZX gene and that both it and gamma, the dnaZ gene product, are integral components of the same enzyme assembly. Hawker, J.R., McHenry, C.S. J. Biol. Chem. (1987) [Pubmed]
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