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The NadABC pathway is involved in the biosynthesis of nicotinamide adenine dinucleotide (NAD) and is a dominant pathway in bacteria. The conversion of l-aspartate to quinolinic acid is initiated by the l-aspartate oxidase NadB, which catalyzes the formation of iminoaspartate that is used by quinolinate synthase NadA in a condensation reaction with dihydroxyacetone phosphate to produce quinolinic acid. NadA is a [4Fesingle bond4S] cluster-containing enzyme that is indispensable in the production of NAD. In B. subtilis, the cysteine sulfurtransferase nifS gene is located in genomic proximity to the nad genes, and its expression is regulated by NadR based on the availability of nicotinic acid. Inactivation of nifS leads to inactivation of the NAD pathway and, consequently, nicotinic acid auxotrophy. In this study, we explored the hypothesis that NifS’ involvement in NAD biosynthesis is associated with its role in the maturation of NadA [4Fesingle bond4S] cluster. We showed through in vitro reconstitution experiments that NifS is catalytically competent in promoting cluster assembly onto apo-NadA and that the rate of reactivation depends on the rate of sulfur mobilization. Furthermore, the activity of NifS in sulfur mobilization is modulated by Apo-NadA. Under conditions of cluster synthesis, apo-NadA enhances the turnover rate of NifS. This phenomenon is not observed for YrvO, NifZ, and SufSU, the other three cysteine sulfurtransferases in B. subtilis. This work provides biochemical evidence for the requirement of a dedicated cysteine desulfurase in the maturation of specialized Fesingle bondS enzymes. 

Cenozoic exhumation in Marie Byrd Land (MBL), West Antarctica, has been dominated by uplift of the MBL dome, an ~800 by ~300 km topographic swell thought to be supported by a hot mantle anomaly, and West Antarctic ice sheet (WAIS) development resulting in deeply incised glacial troughs with up to 3 km of local relief. WAIS expansion is thought to potentially coincide with uplift of the MBL dome, which would have provided the elevated topography necessary to nucleate and grow a continental ice sheet beginning sometime between 34 – 20 Ma. Temporal and spatial relationships between these events remain unclear, however. This study investigates the timing, magnitude, and spatial relationships between tectonic uplift and glacial incision in MBL by leveraging thermo-kinematic modeling informed by detrital low-temperature thermochronology. We investigated Neogene detrital seafloor sediment samples from 14 dredge and core sites along the coast of MBL. Apatite He ages (closure temp ~60°C) of detrital samples range from 23.5 to >80 Ma. Most detrital ages are significantly younger than the ~80 Ma ages typical of exposed bedrock across the region, suggesting these originate from deeply incised bedrock of glacial troughs. The youngest ages obtained for samples retrieved from offshore central and eastern MBL are also significantly younger than the youngest ages obtained for samples from western MBL, suggesting spatial heterogeneity in the timing and/or magnitude of exhumation across the region. Thermo-kinematic modeling of western MBL suggests the regional exhumation rate has been low (10-3 km/myr) since 80 Ma, although focused erosion in glacial troughs produced local late Cenozoic exhumation rates as high as 0.15 km/myr. Preliminary models of the DeVicq glacial trough region of central MBL support these patterns of exhumation. Although model predictions generally agree with observed detrital age distributions, incorporation of detrital ages into these models is expected to provide new insight into the timing of WAIS inception, as well as rates and magnitudes of glacial incision across MBL.