GENETIC CHARACTERIZATION OF LIGC AND LIGD IN MYCOBACTERIAL NHEJ A Dissertation

Abstract

Chromosomal DNA is under constant attack from clastogens that threaten the coding capacity and stability of the genome. Among the wide variety of DNA lesions that the cell must process, Double Strand Breaks (DSBs) of DNA represent a particularly lethal form of DNA damage that must be repaired for chromosome replication and transcription to proceed. The sources of DSBs include ionizing radiation (IR), replication across a single stranded nick [1], DNA processing enzymes that generate DSBs such as topoisomerases, and embedded ribonucleotides in chromosomal DNA [2-5]. As such, the repair of DSBs is a critical function in all living organisms. There are two major pathways of DSB repair: Homologous Recombination (HR) and Non-Homologous End Joining (NHEJ). The most intensely studied and universally distributed pathway of DSB repair is RecA or Rad51 dependent HR, which uses an intact chromosomal template to repair the DSB without mutation. NHEJ is the second pathway that repairs DSBs with little or no use of homology. In contrast to HR, NHEJ is a versatile pathway that uses DNA polymerases and nucleases to restructure the ends and often leads to sequence modification [1]. In eukaryotes, HR is used to repair DSBs during S and G2 phases of the cell cycle when a template copy from sister chromatids is available, whereas NHEJ is active throughout the cell cycle [6]