Opposing roles for 53BP1 during homologous recombination

Although DNA non-homologous end-joining repairs most DNA double-strand breaks (DSBs) in G2 phase, late repairing DSBs undergo resection and repair by homologous recombination (HR). Based on parallels to the situation in G1 cells, previous work has suggested that DSBs that undergo repair by HR predominantly localize to regions of heterochromatin (HC). By using H3K9me3 and H4K20me3 to identify HC regions, we substantiate and extend previous evidence, suggesting that HC-DSBs undergo repair by HR. Next, we examine roles for 53BP1 and BRCA1 in this process. Previous studies have shown that 53BP1 is pro-non-homologous end-joining and anti-HR. Surprisingly, we demonstrate that in G2 phase, 53BP1 is required for HR at HC-DSBs with its role being to promote phosphorylated KAP-1 foci formation. BRCA1, in contrast, is dispensable for pKAP-1 foci formation but relieves the barrier caused by 53BP1. As 53BP1 is retained at irradiation-induced foci during HR, we propose that BRCA1 promotes displacement but retention of 53BP1 to allow resection and any necessary HC modifications to complete HR. In contrast to this role for 53BP1 in HR in G2 phase, we show that it is dispensable for HR in S phase, where HC regions are likely relaxed during replication.     

Dietary Intervention Causes Redistribution of Zinc in Obese Adolescents

Obese people tend to have low zinc circulation levels; this is not always related to zinc intake but can reflect the distribution of zinc in relation to the proportion of body fat and factors related to the inflammatory processes that cause obesity. The purpose of this study was to assess zinc distribution in 15 obese adolescent girls before and after a nutritional orientation program. Participants ranged from 14 to 18 years old (postpubescent) and had a body fat percent (BF%) of >35 %. Zinc nutritional status and other zinc-dependent parameters, such as superoxide dismutase (SOD) and insulin levels, were assessed by biochemical analysis of plasma and erythrocytes, salivary sediment, and urine. Samples were collected before and after 4 months of dietary intervention. Dual energy X-ray absorptiometry (DXA) was used to verify BF% both at the beginning and at the end of the study. Food consumption was assessed in ten individual food questionnaires throughout the study; food groups were separated on the questionnaires in the same way as suggested by some authors to develop the Healthy Eating Index (HEI) but with the addition of zinc. After 4 months of nutritional orientation, 78 % of the participants showed a decrease in BF%. Intraerythrocytic zinc increased over the study period, while salivary sediment zinc, SOD, insulin, and Zn urinary24 h/creatinine all decreased (p?<?0.05). There was no difference in zinc intake throughout the study but participants did increase their consumption of fruits, dairy, and meats during the study (p?<?0.05). There were inverse and statistically significant correlations between the increased levels of intraerythrocytic zinc and decreased levels of SOD. There was also a statistically significant correlation between BF% and Zn urinary 24h/creatinine, and SOD. All these parameters were diminished at the end of the study. The dietary intervention for obese adolescent girls is effective with decrease of BF that led to the redistribution of zinc in the body as shown by the changes in erythrocytes, plasma, salivary, urine zinc, as well as the complementary parameters of insulin and SOD. These changes were not affected by zinc intake.     

Functional characteristics of the maize RNA-binding protein MA16

The maize RNA-binding protein MA16 is a non-ribosomal nucleolar protein widely distributed in different maize tissues. We have previously shown that the MA16 protein binds preferentially to guanosine-and uridine-rich sequences. As a step towards the identification of specific targets with which MA16 interacts within the cell, we investigated the RNA-binding affinities and several other aspects of the protein by using binding assays and immunochemistry. The MA16 protein showed a wide spectrum of RNA-binding activities with lower affinities to several RNAs that was salt and heparin-sensitive indicative of electrostatic interactions, and higher affinities to particular RNAs including rRNA and translatable mRNA sequences. Among the RNAs found associated with MA16 protein was that encoding MA16 itself. This observation raises the possibility that MA16 gene expression could be self-regulated. Immunoprecipitation studies showed that in vivo MA16 was phosphorylated and that MA16 interacts with RNAs through complex association with several proteins. These results suggest that both phosphorylation and interaction with other proteins may be involved in determining RNA-binding specificities of MA16 in the cell.     

Statistical mechanical deconvolution of thermal transitions in macromolecules. III. Application to double-stranded to single-stranded transitions of nucleic acids

The statistical mechanical deconvolution theory for macromolecular conformational transitions is extended to the case of nucleic acids transitions involving strand separation. It is demonstrated that the partition function, Q, as well as all the relevant thermodynamic quantities of the system, can be calculated from experimental scanning calorimetric data. In particular, it is shown that important thermodynamic parameters such as the size of the average cooperative unit during strand separation, the mean helical segment length, and the mean coil-segment length can be calculated from the average excess enthalpy function 〈ΔH〉. The theory is applied to the double-stranded to single-stranded transition of the system poly(A)·poly(U) at different salt concentrations. It is shown that the mean helical segment length is a monotonically decreasing function of the temperature well before strand separation occurs. On the other hand, the mean coil segment length remains practically constant until temperatures very close to T_m. Both experimental findings clearly indicate that the unfolding of poly(A)·poly(U) proceeds through the formation of many short helical sequences. The cooperative unit for the strand separation is calculated to be about 120 base pairs and essentially independent of the salt concentration. The existence of a minimum helical segment length of 10 ± 2 base pairs within the double-stranded form is calculated.     

Revisiting the influence of aggressive interactions on the survival of the first‐laid egg in crested penguins (genus Eudyptes)

Crested penguins Eudyptes spp. have evolved a unique form of breeding in which the first of two eggs laid is much smaller than the second and has a higher likelihood of being lost during egg laying and incubation. In this study, we quantified aggressive behaviour in nesting Snares penguins and undertook an egg survival analysis to examine which factors influence egg loss. During 120 h of observation of 50 nests, we recorded a total of 300 aggressive events in which females were repeatedly pecked, bitten and beaten. Aggressive events lasted from less than a minute to up to 55 min (mean 4.6 ± 7.4 min). Single males were the aggressor in 75% of aggressive events and in 50.7% of aggressive events the aggressor was identified as a neighbouring, breeding male. A greater percentage of the small first eggs (34%) were lost than the large second eggs (4%). We found that egg mortality was influenced by 1) whether the other egg within a nest had hatched, 2) who was present at the nest (father, mother or both) and 3) the average duration of aggressive events on the nest. When one egg within a nest had hatched, the other egg had a vastly increased mortality risk irrespective of aggression. However, long, aggressive events directed towards females after their partners had gone foraging, also increased the probability of egg loss. We suggest that the prolonged nest attendance by breeding males well beyond egg laying is in response to the high frequency of aggressive behaviour during this time. Our data show that A‐egg losses occur due to intraspecific aggression in this species. Further research is needed to clarify whether aggressive behaviour in breeding crested penguins is modulated by elevated testosterone levels in the males and whether any reproductive benefits accrue to the aggressors.     

Enriching the results of screening social life cycle assessment using content analysis: a case study of sugarcane in Brazil

The International Journal of Life Cycle Assessment - Screening social life cycle assessment (S-LCA) can be applied to identify the social hotspots associated with a production activity or supply...     

How policies constrain native seed supply for restoration in Brazil

Large‐scale ecological restoration programs across the world involve a voluminous demand for native seeds of diverse native plant species. In this article, we explore how institutional systems have operated and impacted native seed supply in Brazil. Native seed supply for restoration is essentially a community‐based activity which faces broad barriers to operating within regulations because of requirements for excessive and costly technical documentation, scarcity of seed laboratories, and lack of instructions for native seed quality testing. Although decentralized seed networks have stimulated arrangements for local organizations to promote seed supply, policies constrain the development of local capacities and the ongoing sustainability of these organizations. These conditions have resulted in a vast network of informal collectors and producers who are largely “invisible” and unknown to the regulatory authorities. Policies have decentralized responsibilities from the state without devolving decision‐making power to the multiple stakeholders engaged in policy elaboration. The policies maintain the centralized regulation of native seed supply. After examining Brazilian seed networks' experiences and conducting discussions with stakeholders and experts, we suggest adapting the current regulations to more local level contexts, encompassing the following strategies: (1) ensuring native seed origin and identity; (2) relaxation of the laboratory accreditation process for native seed quality assurance; (3) fostering seed markets for restoration; (4) research to provide technological innovation; (5) supporting local, diverse, and small seed‐based businesses.     

An NAD+ Phosphorylase Toxin Triggers Mycobacterium tuberculosis Cell Death

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Highly hydrophobic biopolymers prepared by the surface pentafluorobenzoylation of cellulose substrates

New highly hydrophobic/lipophobic biopolymers were prepared by the controlled heterogeneous pentafluorobenzoylation of cellulose substrates, i.e., plant and bacterial cellulose fibers. The characterization of the modified fibers was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction, thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angle measurements). The degree of substitution of the ensuing pentafluorobenzoylated fibers ranged from 0.014 to 0.39. The hydrolytic stability of these perfluorinated cellulose derivatives was also evaluated and showed that they were quite water stable, although of course the fluorinated moieties could readily be removed by hydrolysis in an aqueous alkaline medium.