Please see the diagram of NHEJ in my lecture notes.
Here is a summary of the steps of NHEJ, based on my lecture notes. In most cases NHEJ rejoins the correct ends, thus preventing chromosome rearrangements. To accomplish this, the two ends are held together by some unknown mechanism until they can be ligated. This is called "synapsis". Next, Ku heterodimers, which are very abundant, bind to the broken DNA ends. Then DNA-PKcs and Artemis are recruited by Ku. This activates the protein kinase activity of DNA-PKcs, permitting it to phosphorylate Artemis. Phosphorylation greatly stimulates Artemis' endonuclease activity, permitting it to open hairpin loops (if present) and to cut away single-stranded overhangs at DNA ends. Additional nucleases and polymerases may be necessary to process both ends in such a way that they are separated by ligatable nicks (a 3'-OH end adjacent to a 5'-phosphate end). Polynucleotide kinase (PNK) also contributes importantly to end processing (see next question). XRCC4 and DNA ligase IV are also recruited by Ku. XRCC4 recruits PNK and probably polymerase-beta-like polymerases to assist in end processing. Then ligase IV catalyzes the ligation of the two strands. The resulting "healed" DNA molecule is likely to have altered DNA sequence, with the extent of alteration depending on the amount of damage at the break and the extent of processing that was required to make the break ligatable.
For complete credit, I did not expect all the details provided in the paragraph above. However, I did expect the correct names of the major proteins involved, with very brief indications of their roles.
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