"Understanding the Mechanisms Underlying DSB-induced Mutagenesis at Distant Loci in Yeast"

2014 Suddath Award Winner
Natalie Saini
Doctoral Candidate
Kirill Lobachev, PhD, Advisor

Accurate repair of DNA double strand breaks is crucial for the maintenance of genome integrity.  At the same time DSB repair can lead to genome rearrangements and mutagenesis, the hallmarks of cancers and hereditary diseases.  Break induced replication (BIR) is one of the mechanisms employed to repair DSBs with only one ended homology such as those generated upon the collapse of replication forks and at eroded telomeres.  BIR proceeds via invasion of one of the DSB ends into a homologous sequence followed by synthesis of the chromosome arm culminating in a large duplication with a concomitant deletion.   Due to the requirement of large scale DNA synthesis and the utilization of almost all DNA replicative proteins, BIR has been considered analogous to the S-phase replication fork.  However, the bona fide semiconservative mode of synthesis fails to explain the instabilities inherent to BIR.

In this study, we demonstrate that BIR proceeds via an unusual bubble-like replication fork driven by the Pif1 helicase and leading to conservative mode of inheritance for the newly synthesized strands.  Additionally, this non-canonical replication fork generates large single-stranded intermediates indicating that during BIR, the leading strand synthesis occurs via a migrating D-loop followed by lagging strand synthesis.  The presence of extensive single-strandedness suggests that lagging strand synthesis may not be synchronized with leading strand synthesis.  We propose that the structure of the migrating bubble during BIR makes it prone to instabilities including high levels of mutagenesis, increased template switching and generation of half crossovers.

The Parker H. Petit Institute for Bioengineering & Bioscience awards the Suddath Symposium graduate student awards to three students for their grand achievements in biological or biochemical research at the molecular or cellular level.  Lauren Austin, advised by Mostafa El-Sayed, PhD, received the 2nd place award in 2014 for her research in nanobiotechnology and Anthony Awojoodu, a doctoral student in the lab of Edward Botchwey, PhD, was recognized for a 3rd place award for his accomplishments in sickle cell disease research.

Lunch to be served immediately following presentation.