Non-traditional isotopes have become increasingly important as tracers for geological and environmental processes on earth. Recently, renewed attention has been direct towards potassium (K) isotopes given the abundance of K in the earth and the potential for significant mass-dependent fractionation between ⁴¹K and ³⁹K. There is little existing research on K isotopes primarily due to analytical difficulties, however recent technological developments have made precise analysis possible. Seawater has the potential to be an excellent geostandard for K isotope geochemistry because of predicted ⁴¹K/³⁹K homogeneity through the water column, and its wide accessibility around the globe. A total of forty-seven, 30 mL samples were collected in July 2015 aboard the R/V Thomas G. Thompson on the VISIONS 2015 Expedition to Axial Seamount on the Juan de Fuca Ridge. Samples were collected from CTD (Conductivity Temperature Depth) casts as well as niskin bottles operated by the Remotely Operated Platform for Ocean Science (ROPOS). Seawater profile samples were taken at several locations from 7 m down to 2890 m. Evaluating the K isotopic composition at each depth and geographic location will determine if the K isotope composition of seawater is homogeneous and therefore if seawater may be useful as a future geostandard. If K behaves similarly to other non-traditional isotope systems, ³⁹K will preferentially be released into the hydrosphere during weathering, leaving the residual rock enriched in ⁴¹K. This behavior will be useful in constraining the process of granite weathering, and its effect on the K budget in the hydrosphere. In chemical oceanography, there is thought to be a missing sink for K, and it is theorized that clay formation, crustal fractures, or both may remove K from seawater. Determining the feasibility of seawater as a geostandard for K isotopes will further facilitate new research in these and other geochemical topics.

Meier-Gorlin Syndrome (MGS) is a rare form of primordial dwarfism characterized by a short stature, small external ears, and absent kneecaps. Recently, mutations in the pre-replication complex (pre-RC) were linked to MGS. The pre-RC is composed of multiple proteins that must be present in order to initiate DNA replication. Although a genetic link has been made for MGS, it is unclear how these mutations cause the phenotypes observed in humans. To better understand the mutations’ phenotypes on a cellular and molecular level, our lab is utilizing the budding yeast, Saccharomyces cerevisiae. The MGS mutation in the Origin Recognition Complex (ORC) subunit six (ORC6) of the pre-RC occurs in a highly conserved region of the protein where there is a single amino acid substitution (Tyrosine to a Serine) in the C-terminal helix. Since the mutation is conserved from human to yeast, it is predicted that the function of the mutations is also conserved. I introduced the equivalent mutations into budding yeast (orc6^MGS), to investigate the consequences of harboring the MGS mutation on a molecular and cellular level and to elucidate complex genetic interactions these proteins may be involved in. The residues in ORC that recognize origins are unknown. Investigation into this mutation has the potential to illuminate the mechanism behind ORC in eukaryotic cells. The assays performed in this project have exciting implications for the model by which replication initiates and the consequences of a single mutated protein. This genetic approach will hopefully provide insight to how the conserved orc6^MGS mutation is functioning, which has the potential to be translated to the human condition.

DNA replication is essential for cells to divide and is initiated at specific areas along chromosomes called origins. To better understand how perturbing the process of origin initiation affects cells, our lab created a mutant of the Pre Replication Complex in the model organism Saccharomyces cerevisiae. We observe interesting phenotypes in this mutant, including an altered replication pattern and a shortened Chr XII, due to a loss of ribosomal DNA repeats. The rDNA locus contains around 150 copies of a 9.1 kb repeated sequence which encodes the template needed for ribosome synthesis and also an origin of replication, called rARS. We find the activity of rARS is reduced in the mutant and believe the highly repetitive nature of this region and lack of origin initiation make this locus particularly sensitive to replication stress during S-phase. Interestingly, we have found in a different genetic background of yeast, cells harboring this same mutation in the Pre-RC can maintain a relatively large rDNA locus. My research specifically studies this phenomenon and attempts to explore the mechanisms by which this mutant can overcome replication stress in the rDNA region without reducing rDNA copy number. I am currently investigating several possibilities including using gene replacement to determine the role of a notable mutation in a DNA damage repair protein present in this background. This mutation could confer some stress relief to the cells, which would allow them to retain their large rDNA. I will use the genetic tools available in yeast to study this mutation and its effect on rDNA size variation by Pulsed Field Gel Electrophoresis. DNA replication is vital for cell growth and we hope these inquiries will better elucidate the mechanisms and factors involved in replication in order to better our overall understanding of cell biology.