Few, if any, molecules can attest to being more important to life on earth than deoxyribonucleic acid (DNA). Life is based upon this critical molecule, as it defines the structure and function of each individual organism in which it is found. DNA comprises genes, which are responsible for the similarities between closely related organisms, as well as the unique and distinct differences that define individuals in these closely related groups. Such powerful and important responsibilities suggest that DNA must be greatly protected and preserved, and that changes in these critical DNA sequences could have devastating results. DNA sequences do, however, undergo changes and although the consequences of such changes in the genetic code can lead to disaster, there are mechanisms existing within the cell that may properly correct them. Such mechanisms are known collectively as DNA repair and they exist in several different forms (Setlow, 1998). Nucleotide excision repair (NER) is!
             one such mechanism of preserving the DNA sequence and may be considered as not only the frontline of defense for a DNA molecule against sequence-damaging agents, but a possible defense mechanism against many forms of cancer as well.
             Nucleotide excision repair is the method of choice for repairing DNA regions that are damaged by destructive chemical agents. Some forms of error, however, arise by a different means and occur while the DNA sequence is being copied from the parent strand in DNA replication. Such copying errors are recognized by DNA polymerases that scan the molecule for errors in a proofreading capacity. These enzymes recognize incorrect bases in the newly synthesized DNA strand and can subsequently remove them with their 3' to 5' exonuclease activity and replace them with the correct base, utilizing the template strand as a guide. Such a process is referred to as mismatch repair and is the primary mechanism involved in correcting mistakes p...