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. 2015 Apr 30;43(8):4109-20.
doi: 10.1093/nar/gkv217. Epub 2015 Mar 30.

Suppression of the E. coli SOS response by dNTP pool changes

Katarzyna H Maslowska  1 , Karolina Makiela-Dzbenska  2 , Iwona J Fijalkowska  2 , Roel M Schaaper  3
Affiliations

Suppression of the E. coli SOS response by dNTP pool changes

Katarzyna H Maslowska et al. Nucleic Acids Res. .

Abstract

The Escherichia coli SOS system is a well-established model for the cellular response to DNA damage. Control of SOS depends largely on the RecA protein. When RecA is activated by single-stranded DNA in the presence of a nucleotide triphosphate cofactor, it mediates cleavage of the LexA repressor, leading to expression of the 30(+)-member SOS regulon. RecA activation generally requires the introduction of DNA damage. However, certain recA mutants, like recA730, bypass this requirement and display constitutive SOS expression as well as a spontaneous (SOS) mutator effect. Presently, we investigated the possible interaction between SOS and the cellular deoxynucleoside triphosphate (dNTP) pools. We found that dNTP pool changes caused by deficiencies in the ndk or dcd genes, encoding nucleoside diphosphate kinase and dCTP deaminase, respectively, had a strongly suppressive effect on constitutive SOS expression in recA730 strains. The suppression of the recA730 mutator effect was alleviated in a lexA-deficient background. Overall, the findings suggest a model in which the dNTP alterations in the ndk and dcd strains interfere with the activation of RecA, thereby preventing LexA cleavage and SOS induction.

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Figures

Figure 1.
Figure 1.
Microarray analysis on recA730 and related strains. Shown are the log2 values for the fold increase (or decrease) in mRNA expression determined using the Agilent E. coli Gene Expression Microarray System for the indicated comparisons. See the Materials and Methods section for details. Red colors indicate increased gene expression, green color reduced expression. Strains used were EC9428 (wt), EC9461 (dcd), EC9487 (ndk), EC9477 (recA730), EC9471 (recA730 dcd) and EC9503 (recA730 ndk) (see Table 1).
Figure 2.
Figure 2.
dNTP levels in recA730 and related strains. dNTP levels were determined by HPLC analysis as described in the Materials and Methods section. The numbers represent the mean of three independent experiments and are expressed on the Y-axis as milliabsorbance units (A260) measured by the HPLC instrument per OD600 of the bacterial cultures at harvest. Strains used were EC9428 (wt), EC9461 (dcd), EC9487 (ndk), EC9477 (recA730), EC9471 (recA730 dcd) and EC9503 (recA730 ndk) (see Table 1).
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