|Gene:||dnaX||Accession Numbers: EG10245 (EcoCyc), b0470, ECK0464|
The gamma subunit of polymerase III is generated by a programmed frameshift that occurs about half the time and leads to early termination of translation and a protein that lacks the final two domains found in tau. The frameshift occurs in a poly(A) tract and yields a new stop codon immediately following the frameshift signal [Tsuchihashi90, Flower90, Blinkowa90]. Frameshift depends on base pairing between the 3' end of the 16S rRNA and a sequence upstream from the poly(A) tract, as well as the presence of a stable stem loop 3' from the shift point [Larsen94, Larsen97].
The third domain of gamma, which is shared with the tau subunit, is required for oligomerization of both gamma and tau, and also includes the binding sites for delta, delta', chi and psi [Glover01, Gao01b].
Crystal structures of the amino-terminal half of gamma in ATP-bound and unbound states show that ATP binding induces a conformational change that should disrupt dimerization of gamma [Podobnik03].
As described in the gamma subunit description, DnaX undergoes a programmed -1 frameshift roughly half of the time that yields a new stop codon just after the frameshift point [Tsuchihashi90, Flower90, Blinkowa90].
The "Spliced Nucleotide Sequence" link above refers to this frameshifted variant, but note that no splicing occurs.
Gene Citations: [Chen93a]
|Map Position: [491,316 -> 493,247] (10.59 centisomes)||Length: 1932 bp / 431 aa|
Molecular Weight of Polypeptide: 47.545 kD (from nucleotide sequence)
In Paralogous Gene Group: 134 (5 members)
|Cellular Component:||GO:0005737 - cytoplasm
GO:0005829 - cytosol [DiazMejia09]
|MultiFun Terms:||information transfer → DNA related → DNA replication|
|Growth Medium||Growth?||T (°C)||O2||pH||Osm/L||Growth Observations|
|LB Lennox||No||37||Aerobic||7||No [Baba06, Comment 1]|
|Nucleotide-Phosphate-Binding-Region||45 -> 52|
10/20/97 Gene b0470 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG10245; confirmed by SwissProt match.
Baba06: Baba T, Ara T, Hasegawa M, Takai Y, Okumura Y, Baba M, Datsenko KA, Tomita M, Wanner BL, Mori H (2006). "Construction of Escherichia coli K-12 in-frame, single-gene knockout mutants: the Keio collection." Mol Syst Biol 2;2006.0008. PMID: 16738554
Blinkowa90: Blinkowa AL, Walker JR (1990). "Programmed ribosomal frameshifting generates the Escherichia coli DNA polymerase III gamma subunit from within the tau subunit reading frame." Nucleic Acids Res 18(7);1725-9. PMID: 2186364
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Flower90: Flower AM, McHenry CS (1990). "The gamma subunit of DNA polymerase III holoenzyme of Escherichia coli is produced by ribosomal frameshifting." Proc Natl Acad Sci U S A 87(10);3713-7. PMID: 2187190
Gao01b: Gao D, McHenry CS (2001). "Tau binds and organizes Escherichia coli replication proteins through distinct domains. Domain III, shared by gamma and tau, binds delta delta ' and chi psi." J Biol Chem 276(6);4447-53. PMID: 11078742
Glover01: Glover BP, Pritchard AE, McHenry CS (2001). "tau binds and organizes Escherichia coli replication proteins through distinct domains: domain III, shared by gamma and tau, oligomerizes DnaX." J Biol Chem 276(38);35842-6. PMID: 11463787
Larsen97: Larsen B, Gesteland RF, Atkins JF (1997). "Structural probing and mutagenic analysis of the stem-loop required for Escherichia coli dnaX ribosomal frameshifting: programmed efficiency of 50%." J Mol Biol 271(1);47-60. PMID: 9300054
Podobnik03: Podobnik M, Weitze TF, O'Donnell M, Kuriyan J (2003). "Nucleotide-induced conformational changes in an isolated Escherichia coli DNA polymerase III clamp loader subunit." Structure 11(3);253-63. PMID: 12623013
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