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The maintenance of genome stability requires the coordinated actions of multiple proteins and protein complexes. One critical family of proteins is the recombination mediators. Their role is to facilitate the formation of recombinase nucleoprotein filaments on single-stranded DNA (ssDNA). Filament formation can take place on post-replicative ssDNA gaps as well as on 3′-tailed duplexes resulting from helicase–nuclease processing. In prokaryotes, the RecF, O, and R proteins are widely distributed and mediate RecA loading as either the RecFOR or RecOR complexes, depending on the species being studied. In this review, I compare and contrast the available biochemical and structural information to provide insight into the mechanism of action of this critical family of mediators.

The recombination mediator complex RecFOR, consisting of the RecF, RecO, and RecR proteins, is needed to initiate homologous recombination in bacteria by positioning the recombinase protein RecA on damaged DNA. Bacteria from the phylum Campylobacterota, such as the pathogen Campylobacter jejuni, lack the recF gene and trigger homologous recombination using only RecR and RecO. To elucidate the functional properties of C. jejuni RecR (cjRecR) in recombination initiation that differ from or are similar to those in RecF-expressing bacteria, we determined the crystal structure of cjRecR and performed structure-based binding analyses. cjRecR forms a rectangular ring-like tetrameric structure and coordinates a zinc ion using four cysteine residues, as observed for RecR proteins from RecF-expressing bacteria. However, the loop of RecR that has been shown to recognize RecO and RecF in RecF-expressing bacteria is substantially shorter in cjRecR as a canonical feature of Campylobacterota RecR proteins, indicating that cjRecR lost a part of the loop in evolution due to the lack of RecF and has a low RecO-binding affinity. Furthermore, cjRecR features a larger positive patch and exhibits substantially higher ssDNA-binding affinity than RecR from RecF-expressing bacteria. Our study provides a framework for a deeper understanding of the RecOR-mediated recombination pathway.

Osteoblasts are the main functional cells in bone formation, which are responsible for the synthesis, secretion and mineralization of bone matrix. The PI3K/AKT signaling pathway is strongly associated with the differentiation and survival of osteoblasts. The 3-phosphoinositide-dependent protein kinase-1 (PDK-1) protein is considered the master upstream lipid kinase of the PI3K/AKT cascade. The present study aimed to investigate the role of PDK-1 in the process of mouse osteoblast differentiation in vitro. In the BX-912 group, BX-912, a specific inhibitor of PDK-1, was added to osteoblast induction medium (OBM) to treat bone marrow mesenchymal stem cells (BMSCs), whereas the control group was treated with OBM alone. Homozygote PDK1flox/flox mice were designed and generated, and were used to obtain BMSCsPDK1flox/flox. Subsequently, an adenovirus containing Cre recombinase enzyme (pHBAd-cre-EGFP) was used to disrupt the PDK-1 gene in BMSCsPDK1flox/flox; this served as the pHBAd-cre-EGFP group and the efficiency of the disruption was verified. Western blot analysis demonstrated that the protein expression levels of phosphorylated (p)-PDK1 and p-AKT were gradually increased during the osteoblast differentiation process. Notably, BX-912 treatment and disruption of the PDK-1 gene with pHBAd-cre-EGFP effectively reduced the number of alkaline phosphatase (ALP)-positive cells and the optical density value of ALP activity, as well as the formation of cell mineralization. The mRNA expression levels of PDK-1 in the pHBAd-cre-EGFP group were significantly downregulated compared with those in the empty vector virus group on days 3-7. The mRNA expression levels of the osteoblast-related genes RUNX2, osteocalcin and collagen I were significantly decreased in the BX-912 and pHBAd-cre-EGFP groups on days 7 and 21 compared with those in the control and empty vector virus groups. Overall, the results indicated that BX-912 and disruption of the PDK-1 gene in vitro significantly inhibited the differentiation and maturation of osteoblasts. These experimental results provided an experimental and theoretical basis for the role of PDK-1 in osteoblasts.

Replication fork rescue requires Bacillus subtilis RecA, its negative (SsbA) and positive (RecO) mediators, and fork-processing (RadA/Sms). To understand how they work to promote fork remodeling, reconstituted branched replication intermediates were used. We show that RadA/Sms (or its variant, RadA/Sms C13A) binds to the 5′-tail of a reversed fork with longer nascent lagging-strand and unwinds it in the 5′→3′ direction, but RecA and its mediators limit unwinding. RadA/Sms cannot unwind a reversed fork with a longer nascent leading-strand, or a gapped stalled fork, but RecA interacts with and activates unwinding. Here, the molecular mechanism by which RadA/Sms, in concert with RecA, in a two-step reaction, unwinds the nascent lagging-strand of reversed or stalled forks is unveiled. First, RadA/Sms, as a mediator, contributes to SsbA displacement from the forks and nucleates RecA onto single-stranded DNA. Then, RecA, as a loader, interacts with and recruits RadA/Sms onto the nascent lagging strand of these DNA substrates to unwind them. Within this process, RecA limits RadA/Sms self-assembly to control fork processing, and RadA/Sms prevents RecA from provoking unnecessary recombination.

Everglades freshwater marshes were once carbon sinks, but human‐driven hydrologic changes have led to uncertainty about the current state of their carbon dynamics. To investigate the effect of hydrology on CO2 exchange, we used eddy covariance measurements for 2 years (2008–2009) in marl (short‐hydroperiod) and peat (long‐hydroperiod) wetlands in Everglades National Park. The importance of site, season, and environmental drivers was evaluated using linear and nonlinear modeling, and a novel method was used to test for temporally lagged patterns in the data. Unexpectedly, the long‐hydroperiod peat marsh was a small CO2 source (19.9 g C m−2 from July to December 2008 and 80.0 g C m−2 in 2009), and at no time over the study period was it a strong sink. Contrary to previous research suggesting high productivity rates from a short‐hydroperiod marsh, we estimated that the marl site was a small CO2 sink in 2008 (net ecosystem exchange [NEE] = −78.8 g C m−2) and was near neutral for carbon balance in 2009. In addition, both sites had relatively low gross ecosystem exchange (GEE) over the 2 years of this study. The two sites showed similar responses for NEE versus air temperature, ecosystem respiration (Reco) versus air temperature, and Reco versus water depth, although the magnitude of the responses differed. We saw small lags (30 min in most cases) between carbon fluxes and environmental drivers. This study is foundational for understanding the carbon balance of these ecosystems prior to implementation of the planned Everglades restoration of historical water flow that will likely alter the future trajectory of the carbon dynamics of the Everglades as a whole. Key Points Hydrology drives carbon fluxes Freshwater marshes were small sink or small source to our surprise Ecosystem respiration dominated the two ecosystems during our study

A hallmark of human social behavior is the effortless ability to relate one’s own actions to that of the interaction partner, e.g., when stretching out one’s arms to catch a tripping child. What are the behavioral properties of the neural substrates that support this indispensable human skill? Here we examined the processes underlying the ability to relate actions to each other, namely the recognition of spatiotemporal contingencies between actions (e.g., a “giving” that is followed by a “taking”). We used a behavioral adaptation paradigm to examine the response properties of perceptual mechanisms at a behavioral level. In contrast to the common view that action-sensitive units are primarily selective for one action (i.e., primary action, e.g., ‘throwing”), we demonstrate that these processes also exhibit sensitivity to a matching contingent action (e.g., “catching”). Control experiments demonstrate that the sensitivity of action recognition processes to contingent actions cannot be explained by lower-level visual features or amodal semantic adaptation. Moreover, we show that action recognition processes are sensitive only to contingent actions, but not to noncontingent actions, demonstrating their selective sensitivity to contingent actions. Our findings show the selective coding mechanism for action contingencies by action-sensitive processes and demonstrate how the representations of individual actions in social interactions can be linked in a unified representation.

The Escherichia coli RecF, RecO and RecR pro teins have previously been implicated in bacterial recombinational DNA repair at DNA gaps. The RecOR‐facilitated binding of RecA protein to single‐stranded DNA (ssDNA) that is bound by single‐stranded DNA‐binding protein (SSB) is much faster if the ssDNA is linear, suggesting that a DNA end (rather than a gap) facilitates binding. In addition, the RecOR complex facilitates RecA protein‐mediated D‐loop formation at the 5′ ends of linear ssDNAs. RecR protein remains associated with the RecA filament and its continued presence is required to prevent filament disassembly. RecF protein competes with RecO protein for RecR protein association and its addition destabilizes RecAOR filaments. An enhanced function of the RecO and RecR proteins can thus be seen in vitro at the 5′ ends of linear ssDNA that is not as evident in DNA gaps. This function is countered by the RecF/RecO competition for association with the RecR protein.

ABSTRACT The RecA protein is a recombinase functioning in recombinational DNA repair in bacteria. RecA is regulated at many levels. The expression of the recA gene is regulated within the SOS response. The activity of the RecA protein itself is autoregulated by its own C-terminus. RecA is also regulated by the action of other proteins. To date, these include the RecF, RecO, RecR, DinI, RecX, RdgC, PsiB, and UvrD proteins. The SSB protein also indirectly affects RecA function by competing for ssDNA binding sites. The RecO and RecR, and possibly the RecF proteins, all facilitate RecA loading onto SSB-coated ssDNA. The RecX protein blocks RecA filament extension, and may have other effects on RecA activity. The DinI protein stabilizes RecA filaments. The RdgC protein binds to dsDNA and blocks RecA access to dsDNA. The PsiB protein, encoded by F plasmids, is uncharacterized, but may inhibit RecA in some manner. The UvrD helicase removes RecA filaments from RecA. All of these proteins function in a network that determines where and how RecA functions. Additional regulatory proteins may remain to be discovered. The elaborate regulatory pattern is likely to be reprised for RecA homologues in archaeans and eukaryotes.

Agonoscena cisti (Puton, 1882) (Psylloidea, Aphalaridae) is reported for the first time from the Maltese Islands. The species is oligophagous on pistachio plants ( Pistacia L.) and is restricted to the Mediterranean area. Until now, only Agonoscena targionii (Lichtenstein, 1874) had been known from the Maltese archipelago, although the presence of A. cisti was predicted.

ContextInterruption or maintenance of oral antiplatelet therapy (OAT) during an invasive procedure may result in ischaemic and/or haemorrhagic complications. There is currently a lack of clear guidance regarding the issue of treatment interruption during surgical procedures.ObjectiveTo evaluate the rate of major adverse cardiac and cerebrovascular events (MACCEs) and major or minor bleeding complications and their associated independent correlates in coronary stented patients undergoing urgent or planned non-cardiac surgery.Design, setting, and patientsProspective, multicentre, observational cohort study of 1134 consecutive patients with coronary stents.Main outcome measuresThe co-primary endpoints consisted of the incidence of MACCE and major bleeding within the first 30 days of an invasive procedure.ResultsMACCE and haemorrhagic complications were observed in 124 (10.9%) and 108 (9.5%) patients, respectively, within an average time delay from invasive procedure to event of 3.3±3.9 and 5.3±5.3 days. Independent preoperative correlates for MACCE were complete OAT interruption for more than 5 days prior to surgery, preoperative haemoglobin <10 g/dl, creatinine clearance of <30 ml/min and emergency or high-risk surgery. Independent factors for haemorrhagic complications were preoperative haemoglobin <10 g/dl, creatinine clearance between 30 and 60 ml/min, a delay from stent implantation to surgery <3 months and high-risk surgery according to the Lee classification.ConclusionsPatients with coronary stents undergoing an invasive procedure are at high risk of perioperative myocardial infarction including stent thrombosis irrespective of the stent type and major bleeding. Interruption of OAT more than 5 days prior to an invasive procedure is a key player for MACCE.Clinical Trial RegistrationNCT01045850.