Mechanism of nonhomologous end-joining in mycobacteria: a low-fidelity repair system driven by Ku, ligase D and ligase C.
DNA double-strand breaks (DSBs) can be repaired either via homologous recombination (HR) or nonhomologous end-joining (NHEJ). Both pathways are operative in eukaryotes, but bacteria had been thought to rely on HR alone. Here we provide direct evidence that mycobacteria have a robust NHEJ pathway that requires Ku and a specialized polyfunctional ATP-dependent DNA ligase (LigD). NHEJ of blunt-end and complementary 5'-overhang DSBs is highly mutagenic ( approximately 50% error rate). Analysis of the recombination junctions ensuing from individual NHEJ events highlighted the participation of several DNA end-remodeling activities, including template-dependent fill-in of 5' overhangs, nontemplated addition of single nucleotides at blunt ends, and nucleolytic resection. LigD itself has the template-dependent and template-independent polymerase functions in vitro that compose the molecular signatures of NHEJ in vivo. Another ATP-dependent DNA ligase (LigC) provides a backup mechanism for LigD-independent error-prone repair of blunt-end DSBs. We speculate that NHEJ allows mycobacteria to evade genotoxic host defense.
Gong
Chunling
C
Immunology and Molecular Biology Programs, Sloan-Kettering Institute, and Division of Infectious Diseases, Memorial Sloan Kettering Cancer Center, New York, New York 10021, USA.
Bongiorno
Paola
P
Martins
Alexandra
A
Stephanou
Nicolas C
NC
Zhu
Hui
H
Shuman
Stewart
S
Glickman
Michael S
MS
D034961:Antigens, Nuclear / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D000072200:Ku Autoantigen; D009154:Mutation / Q000235:genetics; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011995:Recombination, Genetic / Q000235:genetics*; D013698:Templates, Genetic
D034961:Antigens, Nuclear; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D004247:DNA; D000072200:Ku Autoantigen; D011088:DNA Ligases; D000072481:DNA Ligase ATP