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ligase enzyme that repairs breaks in DNA

microsatellites small repetitive DNA elements dispersed throughout the genome

Next, the double-stranded DNA adjacent to the damage is unwound by a DNA unwinding enzyme called a helicase (Figure 5, step 2). Unwinding of the DNA allows repair proteins access to the site of damage. The DNA strand containing the damaged base is then cleaved a few nucleotides after the damage, and about twenty-five nucleotides before it, by specific endonu-cleases associated with the NER protein complex (Figure 5, step 3). Endonu-cleases are enzymes that cleave inside a segment of DNA.

Next, the DNA segment that contains damage is displaced by DNA poly-merase and associated proteins, and a corresponding repair patch is synthesized (Figure 5, step 4). Lastly, DNA ligase seals the nick, joining the newly synthesized piece of DNA to the preexisting strand (Figure 5, step 5).

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