Mixed Lineage Leukemia 1 (MLL1) protein is a member of the SET1 (or MLL) family of histone methyltransferases. In humans, this family consists of six members: MLL1-4, SETd1A, and SETd1B (1-8). The SET1 family catalyzes methylation of histone 3 lysine 4 (H3K4), 3 an epigenetic mark that is associated with active transcription (9 -12). The human SET1 family is composed of large proteins with several well characterized functional domains involved in chromatin binding and protein-protein interactions (13, 14) (Fig. 1A). Although some of these domains differ among family members, all share a C-terminal SET (suppressor of variegation, enhancer of Zeste, trithorax) domain that confers H3K4 methyltransferase activity (15). Like many chromatin-modifying enzymes, the SET1 family works as part of multiprotein complexes that contain binding partners involved in enzymatic regulation and gene targeting. Although the majority of isolated SET1 family SET domains catalyze weak H3K4 monomethylation (H3K4me1), enhanced methylation is observed in the context of a "core complex" (16). The minimal core complex required for enhanced methylation is composed of the SET1/MLL SET domain and a subcomplex called WRAD (WD-40 repeat protein 5 (WDR5), retinoblastoma-binding protein 5 (RbBP5), absent small homeotic 2-like (ASH2L), and dumpy-30 (DPY-30)) (17)(18)(19)(20). Interestingly, SET1 family core complexes preferentially catalyze different levels of H3K4 methylation in a manner that correlates with their evolutionary lineage (16). Whereas SETd1A/B core complexes catalyze mono-, di-, and trimethylation of H3K4 (H3K4me1, H3K4me2, and H3K4me3, respectively), the MLL1 and MLL4 (also known as MLL2) core complexes predominantly catalyze mono-and dimethylation (16). In contrast, MLL2 and MLL3 core complexes catalyze predominantly H3K4 monomethylation (16). In cells, different levels of H3K4 methylation are localized to distinct genomic regions and are associated with distinct functional outcomes (21-23). Assembly of the MLL1 core complex requires a direct interaction between MLL1 and WDR5, whereby WDR5 acts to stabilize the interaction between the MLL1 SET domain and the RbBP5/ASH2L heterodimer (18,24). The MLL1-WDR5 interaction occurs via the conserved Win (WDR5 interaction) * This work was supported, in whole or in part, by the National Institutes of Health Grant R01CA140522 (to M. S. C.). The authors declare that they have no conflicts of interest with the contents of this article. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Coupling recent advancements in genetic engineering of diverse microbes and gas-driven fermentation provides a path towards sustainable commodity chemical production. Cupriavidus necator H16 is a suitable species for this task because it effectively utilizes H 2 and CO 2 and is genetically tractable. Here, we demonstrate the versatility of C. necator for chemical production by engineering it to produce three products from CO 2 under lithotrophic conditions: sucrose, polyhydroxyalkanoates (PHAs), and lipochitooligosaccharides (LCOs). We engineered sucrose production in a co-culture system with heterotrophic growth 30 times that of WT C. necator . We engineered PHA production (20-60% DCW) and selectively altered product composition by combining different thioesterases and phaCs to produce copolymers directly from CO 2 . And, we engineered C. necator to convert CO 2 into the LCO, a plant growth enhancer, with titers of ~1.4 mg/L-equivalent to yields in its native source, Bradyrhizobium . We applied the LCOs to germinating seeds as well as corn plants and observed increases in a variety of growth 1

Polyphosphates (polyPs) are ubiquitous polymers in living organisms from bacteria to mammals. They serve a wide variety of biological functions, ranging from energy storage to stress response. In the last two decades, polyPs have been primarily viewed as linear polymers with varying chain lengths. However, recent biochemical data show that small metaphosphates, cyclic oligomers of [PO3](−), can bind to the enzymes ribonuclease A and NAD kinase, raising the question of whether metaphosphates can occur naturally as products of biological activity. Before the 1980s, metaphosphates had been reported in polyPs extracted from various organisms, but these results are considered artifactual due to the extraction and purification protocols. Here, we employ nondestructive 31P solid-state NMR spectroscopy to investigate the chemical structure of polyphosphates in whole cells as well as insoluble fractions of the bacterium Xanthobacter autotrophicus. Isotropic and anisotropic 31P chemical shifts of hydrated whole cells indicate the coexistence of linear and cyclic phosphates. Under our cell growth conditions and the concentrated conditions of the solid-state NMR samples, we found substantial amounts of cyclic phosphates in X. autotrophicus, suggesting that in fresh cells metaphosphate concentrations can be significant. The cellular metaphosphates are identified by comparison with the 31P chemical shift anisotropy of synthetic metaphosphates of known structures. In X. autotrophicus, the metaphosphates have a chemical shift anisotropy that is consistent with an average size of 3–8 phosphate units. These metaphosphates are enriched in insoluble and electron-dense granules. Exogenous hexametaphosphate added to X. autotrophicus cell extracts is metabolized to trimetaphosphates, supporting the presence and biological role of metaphosphates in cells. The definitive evidence for the presence of metaphosphates, reported here in whole bacterial cells for the first time, opens the path for future investigations of the biological function of metaphosphates in many organisms.

Coupling recent advancements in genetic engineering of diverse microbes and gas-driven fermentation provides a path towards sustainable commodity chemical production. Cupriavidus necator H16 is a suitable species for this task because it effectively utilizes H 2 and CO 2 and is genetically tractable. Here, we demonstrate the versatility of C. necator for chemical production by engineering it to produce three products from CO 2 under lithotrophic conditions: sucrose, polyhydroxyalkanoates (PHAs), and lipochitooligosaccharides (LCOs). We engineered sucrose production in a co-culture system with heterotrophic growth 30 times that of WT C. necator . We engineered PHA production (20-60% DCW) and selectively altered product composition by combining different thioesterases and phaCs to produce copolymers directly from CO 2 . And, we engineered C. necator to convert CO 2 into the LCO, a plant growth enhancer, with titers of ~1.4 mg/L-equivalent to yields in its native source, Bradyrhizobium . We applied the LCOs to germinating seeds as well as corn plants and observed increases in a variety of growth

Intracellular cargo delivery is a critical and challenging step in controlling cell states. Silicon nanowire (NW) arrays have emerged as a powerful platform for accessing the intracellular space through a combination of their nanoscale dimensions and electrical properties. Here, we develop and characterize a conductive polypyrrole (PPy)-NW device for temporally controlled intracellular delivery. Fluorescent cargos, doped in electroresponsive PPy matrices at wire tips as well as entire NW arrays, are released with an applied reducing potential. Intracellular delivery into endothelial cells from PPy-Si substrates demonstrated comparable kinetics to solution-based delivery methods while requiring an order of magnitude less cargo loading. This hybrid polymer–semiconductor platform extends methods available for intracellular delivery and links electrical signaling from artificial systems with living molecular transduction.

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Crystalline metal oxide catalysts operating under oxygen evolution reaction (OER) conditions invariably restructure, resulting in active sites with hydroxo/oxo species in an amorphous environment. An increase in the population of terminal hydroxo/oxo species (i.e., edge sites) facilitates proton-coupled electron-transfer (PCET) kinetics for oxygen generation and thus improves catalyst competency. While amorphous films benefit from a greater density of active sites, they suffer from diminished charge transport as compared to that of extended crystalline lattices. Managing this amorphous–crystalline dichotomy is essential when designing OER catalysts, which we highlight with the examination of electrodeposited PbO x materials, which historically are very poor OER catalysts. Along these lines, the presence of phosphate during PbO x electrodeposition truncates the growth of an extended lattice owing to its strong bonding to oxide surfaces to afford an amorphous catalyst film (A-PbO x ) with significant charge-transfer resistance (138 ± 42 Ω) and poor OER kinetics (420 ± 105 mV dec–1 Tafel slope). Conversely, electrodeposition of Pb2+ in the presence of less coordinating electrolytes such as nitrate affords crystalline β-PbO2 with improved charge-transfer resistance (42.6 ± 1.1 Ω), though still poor OER kinetics (134 ± 36 mV dec–1 Tafel slope). By operating amorphous A-PbO x in less coordinating electrolytes, however, a new partially crystalline material can be generated (μc-PbO x ) with further reduced charge-transfer resistance (33.0 ± 1.4 Ω) and improved OER kinetics (70 ± 15 mV dec–1 Tafel slope). The enhanced OER activity of μc-PbO x is the result of coupling the high edge-site population of an amorphous PbO x phase with crystalline-like charge transport properties. The ability to use an electrolyte to induce OER activity in an inactive amorphous form of PbO x highlights the benefits of optimizing the amorphous–crystalline phase compositions in the design of active OER catalysts.

SUMMARYThe synthesis of mitochondrial DNA (mtDNA) is not coupled with cell cycle. Previous studies have shown that the size of deoxyribonucleoside triphosphate (dNTP) pools plays an important role in regulating mtDNA replication and amplification. In yeast, dNTPs are synthesized by the cytosolic ribonucleotide reductase (RNR). It is currently poorly understood as to how RNR activity is regulated in non-dividing or quiescent cells to finely tune mtDNA metabolism to cope with different metabolic states. Here, we show that defect in the 20S proteasome drastically destabilizes mtDNA. The mtDNA instability phenotype in 20S proteasome mutants is suppressed by overexpression of RNR3 or by the deletion of SML1, encoding a minor catalytic subunit and an intrinsic inhibitor of RNR respectively. We found that Sml1 is stabilized in the 20S proteasomal mutants, suggesting that 20S affects mtDNA stability by stabilizing Sml1. Interestingly, defect in the regulatory 19S proteasomal function has only subtle effect on mtDNA stability, supporting a role of the 20S proteasome in dNTP homeostasis independent of 19S. Finally, we found that when cells are transitioned from glycolytic to oxidative growth, Sml1 level is reduced in a 20S-dependent manner. In summary, our study establishes a link between cellular proteostasis and mtDNA metabolism through the regulation of dNTP homeostasis. We propose that increased degradation of Sml1 by the 20S proteasome under respiratory conditions provides a mechanism to stimulate dNTP synthesis and promote mtDNA amplification.