Factors increasing the flexibility of nonhomologous end joining

Last Modified

Creator

Waters, Crystal
- Affiliation: School of Medicine, Curriculum in Genetics and Molecular Biology

Abstract

Broken chromosomes can be catastrophic for an organism if misrepaired or left unrepaired. Mammals rely predominately on non-homologous end joining (NHEJ) to efficiently repair chromosome breaks, which arise as programmed intermediates to cellular processes such V(D)J recombination or arise due to cellular damage. These sources can generate a variety of end structures often lacking sequence complementarity or containing nucleotide damage. I determined that NHEJ makes use of low fidelity direct ligation to bypass subtle mispairs and radiomimetic damage. This allows cells to avoid the consequences of an unrepaired double strand break, while allowing other repair pathways to subsequently fix the retained damage. In cases where direct ligation is impeded, NHEJ employs end-processing factors (e.g. polymerases and nucleases) to modify ends until they are ligatable. I found that end processing proceeds nonrandomly and is driven largely by the initial end structure. I found that the gaps created by aligning the ends were filled by DNA Pol λ and Pol μ, making them critical for the repair of incompatible ends. The two polymerases were found to have distinct activities and to be preferentially active on distinct substrates. Interestingly, I found that these polymerases also have a key role nuclease-dependent resolution by NHEJ. This work has shown that NHEJ systematically adapts to different end structures, which demonstrates just how sophisticated and flexible this pathway is.

Date of publication