SOS response, in E. coli

TABLE 25-6 Genes Induced as Part of the SOS Response in E. coli... 

Repressors and Repression How would the SOS response in E. coli be affected by a mutation in the lexA gene that prevented autocatalytic cleavage of the LexA protein ... 

Figure 22.22. SOS response in E. coli. Under normal growth conditions (SOS off), genes under the SOS control are repressed by the LexA repressor. DNA damage or replication block triggers SOS response, leading to activation of the RecA co-protease and subsequent inactivation of the LexA repressor by RecA-assisted auto cleavage. This results in induced transcription of the various SOS genes (SOS on). Combined cellular activities such as DNA repair and translesion synthesis eventually removes the SOS signal. Consequently, the RecA co-protease is inactivated and the LexA repressor is accumulated in cells, returning cells to the SOS off state.

Koffel-Schwartz, N., Coin, F., Veaute, X., and Fuchs, R. P. P. (1996). Cellular strategies for accomodating replication-hindering adducts in DNA Control by the SOS response in E. coli. Proc. Natl Acad. Sci. USA 93, 7805-7810. 

A large number of proteins involved in DNA repair, recombination and replication have been shown to be induced when required (18-20). The SOS response in E. coli, which coordinates the expression of over twenty genes, is probably the best understood model system demonstrating the functional orientation of transcriptionally induced genes (21). This response to... 

Bacteria are smaller than protozoa and are responsible for many diseases, such as typhoid fever, cholera, diarrhea, and dysentery. Pathogenic bacteria range in size from 0.2 to 0.6 /tm, and a 0.2 /tm filter is necessary to prevent transmission. Contamination of water supplies by bacteria is blamed for the cholera epidemics, which devastate undeveloped countries from time to time. Even in the U.S., E. coli is frequently found to contaminated water supplies. Fortunately, E. coli is relatively harmless as pathogens go, and the problem isn t so much with E. coli found, but the fear that other bacteria may have contaminated the water as well. Never the less, dehydration from diarrhea caused by E. coli has resulted in fatalities. 

Polymerases of Class B. Although E. coli polymerase II is a member of this family, relatively little is known about its function. It may participate in DNA repair in the "SOS" response (Section E).265... 

In E. coli, DNA damage-induced mutagenesis is tightly controlled by the SOS regulatory system. Eukaryotes, on the other hand, do not contain a similar SOS response system. Nevertheless, translesion synthesis and base damage-induced mutagenesis are controlled in eukaryotic cells at two levels. First, the bypass polymerases are controlled to a low concentration in cells. Second, the extent by which translesion synthesis contributes to damage tolerance is controlled in cells. 

In a recent study it was reported that luminescence reporters could be detected at lower concentrations and with a faster response time compared with fluorescent reporter proteins. In E. coli there is negligible luminescence background but a considerable autofluorescence background, so that larger amounts of protein are required to overcome background levels (Hakkila et al., 2002). 

An example for autoregulation is found in the hut-operon of E. coli and in the regulation of the SOS response in bacteria via the lexA repressor. There are examples of autoregulation at the level of translation as well (see Section 1.5.5.1). 

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