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Review
. 2008 Sep 23;4(6):338-44.
doi: 10.7150/ijbs.4.338.

Inducible SOS response system of DNA repair and mutagenesis in Escherichia coli

Celina Janion  1
Affiliations
Review

Inducible SOS response system of DNA repair and mutagenesis in Escherichia coli

Celina Janion. Int J Biol Sci. .

Abstract

Chromosomal DNA is exposed to continuous damage and repair. Cells contain a number of proteins and specific DNA repair systems that help maintain its correct structure. The SOS response was the first DNA repair system described in Escherichia coli induced upon treatment of bacteria with DNA damaging agents arrest DNA replication and cell division. Induction of the SOS response involves more than forty independent SOS genes, most of which encode proteins engaged in protection, repair, replication, mutagenesis and metabolism of DNA. Under normal growth conditions the SOS genes are expressed at a basal level, which increases distinctly upon induction of the SOS response. The SOS-response has been found in many bacterial species (e.g., Salmonella typhimurium, Caulobacter crescentus, Mycobacterium tuberculosis), but not in eukaryotic cells. However, species from all kingdoms contain some SOS-like proteins taking part in DNA repair that exhibit amino acid homology and enzymatic activities related to those found in E. coli. but are not organized in an SOS system. This paper presents a brief up-to-date review describing the discovery of the SOS system, the physiology of SOS induction, methods for its determination, and the role of some SOS-induced genes.

Keywords: DNA mutations; DNA repair; SOS response; error-prone repair; mutagenic DNA polymerases.

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Conflict of interest statement

Conflict of Interest: The author has declared that no conflict of interest exists.

Figures

Figure 1
Figure 1
Kinetics of induction of β-galactosidase in din::lacZ fusion strains by mitomycin C (MC) . The din::lac fusions were generated by the insertion of the Mu d1(Ap, lac) bacteriophage into the E. coli chromosome. The λ::Mu d1(Ap lac) derivative was generated by an insertion of Mu d1(Ap lac) in the λ phage into E. coli chromosome. Symbols: o, untreated fusion strain; ●, fusion strains plus MC; lexA(Ind-) derivatives of the fusion strain plus MC; ■, recA (Def) derivatives of the fusion strain plus MC; ▼, a pKM280-containing derivative of the of the λ:: Mu d1(Ap lac) strain plus MC. Reprinted from with author's permission. Two of genes, dinA and dinB were subsequently identified as polB (Pol II) and Pol IV, respectively , , .
Figure 2
Figure 2
Northern analysis of E. coli genes that appear to be regulated by LexA. RNA was extracted from three isogenic strains that differed in lexA gene: RW118 (lexA+), RW434 (lexA[Ind-]), and RW542 (lexA51[Def]). RNA was obtained from undamaged cells (-) and from cells that had been exposed to mitomycin C (5 µg ml-1) (+) for 30 min before extraction. The previously identified LexA-regulated recA and umuDC genes were used as positive controls. The genes are depicted according to their ascending heterology index (HI). The sizes of the mRNA transcript and the possible functions of the genes are also indicated See ref. for more details. (By courtesy of Blackwell Science).
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