[SigE inhibits DNA damage and participates in the regulation of DNA damage repair in Mycobacterium smegmatis].

Abstract

Objective To investigate the anti-DNA damage role of Sigma factor E (SigE) and its regulation mechanism of DNA damage repair in Mycobacterium smegmatis(MS). Methods The SigE gene of Mycobacterium smegmatis was cloned into plasmid pMV261 to construct recombinant plasmid pMV261(+)-SigE, and the inserted gene was verified by sequencing. The recombinant plasmid was electrically transformed into Mycobacterium smegmatis to construct SigE over-expression strain, and the expression of SigE was detected by Western blot analysis. The Mycobacterium smegmatis containing pMV261 plasmid was used as the control strain. Growth differences between the two stains were monitored by measuring the 600 nm absorbance (A₆₀₀) value of the bacterial culture suspension. The survival rate differences between two kinds of strains which were treated with three kinds of DNA damaging agents including ultraviolet ray (UV), cisplatin (DDP), and mitomycin C (MMC) were detected by colony forming unit (CFU) counting assay. DNA damage repair pathways of Mycobacteria were analyzed through bioinformatics and SigE-related genes were screened. The relative expression levels of these genes possibly related to the SigE against DNA damage were detected by real-time fluorescence quantitative PCR. Results SigE over-expression strain pMV261(+)-SigE/MS was constructed and the expression of SigE in Mycobacterium smegmatis was detected. Compared with the control strain, the SigE over-expression strain grew more slowly and entered the growth plateau later; survival rate analysis found that SigE over-expression strain was more resistant to three DNA damaging agents including UV, DDP, and MMC. Bioinformatic analysis indicated that SigE gene was closely related to DNA damage repair genes recA, single-strand DNA binding protein, (ssb), and dnaE2; the expression levels of recA, dnaE2, and ssb in SigE over-expression strain all increased with varying degrees compared with those in the control strain. Conclusion SigE plays an important role in inhibiting the DNA damage of Mycobacterium smegmatis, whose mechanism is closely related to the regulation of DNA damage repair.