Computational analysis of LexA regulons in species.

To gain a general understanding of the SOS system in species, in this study LexA-binding sites and the LexA regulons in 23 genomes were first predicted by phylogenetic footprinting server, then with as an example, the expression of LexA regulon in iron limitation was investigated by proteomic analysis and quantitative reverse transcription polymerase chain reaction (RT-qPCR) method. The results showed that LexA proteins were highly conserved in species, and were in a close phylogenetic relationship with those in Gram-negative bacteria; the core SOS response genes and were found in all the 23 genomes, indicating that this system was widely distributed in this genus; besides that, putative LexA-binding sites were also found in the upstream sequences of some genes involved in other biological processes such as biosynthesis, drug resistance, and stress response. Proteomic and RT-qPCR analyses showed that under iron deficient condition, the expression of , and was transcriptionally upregulated ( < 0.05), was also translationally upregulated but was on the contrary ( < 0.05), whereas another SOS response gene was transcriptionally downregulated ( < 0.01). These results indicated that in response to iron deficiency, the members of LexA regulon were not regulated by the same way, suggesting the existence of a precise regulation mechanism of SOS response in . In conclusion, this study provided a preliminary understanding of the SOS system in species, which laid the foundation for further investigation of its roles in SOS response and other biological processes.