FIG 1.

Models for bacterial NHEJ. (A) The minimal NHEJ system in bacteria has only two proteins, Ku (shown in purple) and LigD (shown in blue). LigD possesses all of the activities required to clean, process, and ligate DSBs. (B) The LigD-LIG-independent pathway consists of a polymerase (LigD-POL, PolD1, or PolD2) and LigC. (C) In M. smegmatis, NHEJ may require Ku and multiple polymerases (LigD-POL, PolD1, and PolD2) and ligases (LigD-LIG and LigC) in addition to RNase HII to remove the residual ribonucleotide left over after the DSB is repaired.