Understanding the biosynthesis of human IgM SAM-6 through a combinatorial expression of mutant subunits that affect product assembly and secretion.

Polymeric IgMs are secreted from plasma cells abundantly despite their structural complexity and intricate multimerization steps. To gain insights into IgM's assembly mechanics that underwrite such high-level secretion, we characterized the biosynthetic process of a natural human IgM, SAM-6, using a heterologous HEK293(6E) cell platform that allowed the production of IgMs both in hexameric and pentameric forms in a controlled fashion. By creating a series of mutant subunits that differentially disrupt secretion, folding, and specific inter-chain disulfide bond formation, we assessed their effects on various aspects of IgM biosynthesis in 57 different subunit chain combinations, both in hexameric and pentameric formats.

Enameloid-bound δ N reveals large trophic separation among Late Cretaceous sharks in the northern Gulf of Mexico.

The nitrogen isotopic composition ( N/ N ratio, or δ N) of enameloid-bound organic matter (δ N ) in shark teeth was recently developed to investigate the biogeochemistry and trophic structures (i.e., food webs) of the ancient ocean.

Cenozoic megatooth sharks occupied extremely high trophic positions.

Trophic position is a fundamental characteristic of animals, yet it is unknown in many extinct species. In this study, we ground-truth the N/N ratio of enameloid-bound organic matter (δN) as a trophic level proxy by comparison to dentin collagen δN and apply this method to the fossil record to reconstruct the trophic level of the megatooth sharks (genus ). These sharks evolved in the Cenozoic, culminating in , a shark with a maximum body size of more than 15 m, which went extinct 3.

regulates the kinetics of heat-induced expression in Arabidopsis.

Arabidopsis contains four heat shock transcription factors ( , , , and ) that regulate the primary response to high temperature stress responses. These genes have overlapping functions and, while double and triple mutants have thermotolerance phenotypes, these genes have no reported single mutant thermotolerance phenotypes. We used an automated fluorescence microscopy system to quantitate the expression of a 6:GFP reporter with high temporal resolution to show that is required for normal heat-induced expression.