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Section: Genetics » Chemistry of the Gene » Synthesis, Modification and Repair of DNA
 
 
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  An SOS repair system in E. coli
 
     
 
Content
⇒ Chemistry of the Gene 2.  Synthesis, Modification and Repair of DNA
⇒ DNA replication: general features 
⇒ Semi-conservative DNA replication in E. coli
⇒ Semi-conservative replication of chromosomes in eukaryotes
⇒ Semi-discontinuous DNA replication
⇒ Unidirectional and bidirectional DNA replication
⇒ RNA primers in DNA replication
⇒ Regulation of DNA replication by anti-sense RNA primer
⇒ Prokaryotic DNA polymerases
⇒ Eukaryotic DNA polymerases
⇒ Replicons for DNA replication
⇒ DNA replication in prokaryotes 
⇒ Experimental approaches for the study of DNA replication
⇒ Initiation of DNA replication
⇒ Elongation of DNA chain
⇒ Replication fork movement
⇒ Termination of DNA replication
⇒ DNA replication in eukaryotes 
⇒ DNA replication and cell cycle
⇒ Replication origins and initiation of DNA replication (cis and trans-acting elements)
⇒ Comparison of initiation of DNA replication with transcription initiation
⇒ Different steps involved in eukaryotic DNA replication
⇒ Synthesis of telomeric DNA by telomerase
⇒ Models of DNA replication
⇒ Replication fork model
⇒ Rolling circle model of DNA replication
⇒ Mitochondrial DNA replication and D-loops
⇒ RNA directed DNA synthesis (reverse transcription)
⇒ DNA modification and DNA restriction
⇒ DNA repair
⇒ Excision repair systems in E. coli
⇒ An SOS repair system in E. coli
⇒ DNA repair and genetic diseases in humans
An SOS repair system in E. coli
In E. coli, many treatments causing DN/ damage or inhibition of DNA replication, induce a complex series of phenotypic changes described as SOS response. The SOS response (increased capacity to repair damaged DNA) is initiated by interaction of RecA protein with LexA repressor. Following steps are involved : (i) damaging treatment activates RecA protein (a protease), through common intermediates (small DNA molecules or single stranded region); (ii) RecA protease interacts with LexA repressor (coded by lex A gene) and due to proteolytic action of RecA on LexA, all operons to which LexA is bound are induced (Fig. 26.35); these may include a number of operons/genes called din (damage inducible) genes, such as uvr A, uvr B, uvr C and hin A. These genes each has a SOS box, 20 bp long having a 8 bp long consensus sequence. Since LexA represses its own synthesis and that of RecA, its proteolytic degradation leads to amplification of both LexA and RecA proteins. However, when DNA damaging signal is removed, RecA is not induced and LexA accumulates, which represses all other genes belonging to SOS system.

The SOS DNA repair system in E. coli.
Fig. 26.35. The SOS DNA repair system in E. coli.

 
     






     
     
 
 
     
 
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