Atypical Role for PhoU in Mutagenic Break Repair under Stress in Escherichia coli
Fig 4
PhoU is required for MBR in the E. coli chromosome.
(A) Diagram of relevant genetic elements in the E. coli chromosome. Experimental design of [16]. Cells expressing a chromosomal regulatable I-SceI endonuclease gene and carrying a chromosomal cutsite near a tet +1bp frameshift allele are starved in liquid for 84 hours (with no tetracycline), rescued to rich medium then plated on rich tetracycline and no-drug plates to score tetracycline-resistant (TetR) mutant colonies. (B) PhoU is required for I-SceI-induced MBR under stress, and DSBs do not substitute for PhoU in mutagenesis. DSB strains have I-SceI enzyme and cutsite and control “No-DSB” strains have I-SceI cutsite only. Strains: “No-DSB”, SMR10865; DSB, SMR10866; phoU DSB, SMR20344. The DSB mutant frequency is 14.5 TetR mutants /108 cells (1.5 x 10-7 TetR mutants per cell). Mean ± range of two independent experiments.