Maruyama, R. | bioRxiv Science

bioRxiv2018

HERC2 promotes BLM and WRN to suppress G-quadruplex DNA

BLM and WRN are RecQ DNA helicases essential for genomic stability. Here we demonstrate that HERC2, a HECT E3 ligase, is critical for their functions to suppress G-quadruplex (G4) DNA. HERC2 interacts with BLM, WRN, and replication protein A (RPA) complexes during S-phase of the cell cycle. Depletion of HERC2 dissociates RPA from BLM and WRN complexes and significantly increases G4 formation. Triple depletion revealed that HERC2 has an epistatic relationship with BLM and WRN in their G4- suppressing function. In vitro, HERC2 releases RPA onto single-stranded DNA (ssDNA), rather than anchoring onto RPA-coated ssDNA. CRISPR/Cas9-mediated deletion of the catalytic ubiquitin-binding site of HERC2 causes RPA accumulation in the helicase complexes and increases G4, indicating an essential role for E3 activity in G4 suppression. Both HERC2 depletion and E3 inactivation sensitize cells to the G4-interacting compounds, telomestatin and pyridostatin. Overall, HERC2 is a master regulator of G4 suppression and affects the sensitivity of cells to G4 stabilizers.

molecular biology↗

bioRxiv2018

Soil nutrient stoichiometry affects the initial response of microbial community to trophic perturbation.

Soil microbes are drivers of global ecosystem functionality and are continuously subjected to external perturbations. It is fundamental for ecologists and environmental scientists to understand and further predict the microbes responses to these perturbations. A major and ubiquitous perturbation is the addition of chemical nutrients, including fertilizers and animal urine, to soil. Recent biogeographical studies suggest that soil nutrient stoichiometry (i.e., nutritional balance) determines microbial community structure and its functions with regard to material circulation. Given this information, here, we show that soil nutrient stoichiometry, or the bioavailable C:P ratio, determines the impact of nutrient addition on the soils microbial communities. We sampled two soils with similar carbon and nitrogen concentrations but with a 20-fold difference in phosphorus bioavailability. Soil microcosms with carbon and nitrogen amendments were constructed for both the soils. The phosphorus-depleted soil received prolonged effect from carbon and nitrogen amendments: the phosphatase activity gradually increased over a 24-day incubation period and the microbial community structure did not present recovery to its initial state. In contrast, in the other soil, both phosphatase activity and microbial community structure gradually returned to those of the control samples. Phosphorus depletion mitigated carbon and nitrogen intake; therefore, the effects of carbon and nitrogen amendment lasted longer. Our results demonstrate that nutritional stoichiometry is a strong predictor of microbial community dynamics in response to trophic perturbation, particularly when considering the length of time the trait of perturbation persists in the soil.

ecology↗