Bacterial single-stranded (ss)DNA-binding proteins (SSB) are essential for the replication and maintenance of the genome. SSBs share a conserved ssDNA-binding domain, a less conserved intrinsically disordered linker (IDL), and a highly conserved C-terminal peptide (CTP) motif that mediates a wide array of protein−protein interactions with DNA-metabolizing proteins. Here we show that the Escherichia coli SSB protein forms liquid−liquid phase-separated condensates in cellular-like conditions through multifaceted interactions involving all structural regions of the protein. SSB, ssDNA, and SSB-interacting molecules are highly concentrated within the condensates, whereas phase separation is overall regulated by the stoichiometry of SSB and ssDNA. Together with recent results on subcellular SSB localization patterns, our results point to a conserved mechanism by which bacterial cells store a pool of SSB and SSB-interacting proteins. Dynamic phase separation enables rapid mobilization of this protein pool to protect exposed ssDNA and repair genomic loci affected by DNA damage.

Cells must continuously repair inevitable DNA damage while avoiding the deleterious consequences of imprecise repair. Distinction between legitimate and illegitimate repair processes is thought to be achieved in part through differential recognition and processing of specific noncanonical DNA structures, although the mechanistic basis of discrimination remains poorly defined. Here, we show that Escherichia coli RecQ, a central DNA recombination and repair enzyme, exhibits differential processing of DNA substrates based on their geometry and structure. Through single-molecule and ensemble biophysical experiments, we elucidate how the conserved domain architecture of RecQ supports geometry-dependent shuttling and directed processing of recombination-intermediate [displacement loop (D-loop)] substrates. Our study shows that these activities together suppress illegitimate recombination in vivo, whereas unregulated duplex unwinding is detrimental for recombination precision. Based on these results, we propose a mechanism through which RecQ helicases achieve recombination precision and efficiency.RecQ | helicase | magnetic tweezers | single molecule | DNA unwinding

In this paper we examine numerically the Gallavotti-Cohen fluctuation formula for phase-space contraction rate and entropy production rate fluctuations in the Nosé-Hoover thermostated periodic Lorentz gas. Our results indicate that while the phase-space contraction rate fluctuations violate the fluctuation formula near equilibrium states, the entropy production rate fluctuations obey this formula near and far from equilibrium states as well.

The microbiota and microbiome and disruption of the gut-brain axis were linked to various metabolic, immunological, physiological, neurodevelopmental, and neuropsychiatric diseases. After a brief review of the relevant literature, we present our hypothesis that intestinal serotonin, produced by intestinal enterochromaffin cells, picked up and stored by circulating platelets, participates and has an important role in the regulation of membrane permeability in the intestine, brain, and other organs. In addition, intestinal serotonin may act as a hormone-like continuous regulatory signal for the whole body, including the brain. This regulatory signal function is mediated by platelets and is primarily dependent on and reflects the intestine’s actual health condition. This hypothesis may partially explain why gut dysbiosis could be linked to various human pathological conditions as well as neurodevelopmental and neuropsychiatric disorders.

The single-stranded DNA binding protein (SSB) of Escherichia coli plays essential roles in maintaining genome integrity by sequestering ssDNA and mediating DNA processing pathways through interactions with DNA-processing enzymes. Despite its DNA-sequestering properties, SSB stimulates the DNA processing activities of some of its binding partners. One example is the genome maintenance protein RecQ helicase. Here, we determine the mechanistic details of the RecQ–SSB interaction using single-molecule magnetic tweezers and rapid kinetic experiments. Our results reveal that the SSB–RecQ interaction changes the binding mode of SSB, thereby allowing RecQ to gain access to ssDNA and facilitating DNA unwinding. Conversely, the interaction of RecQ with the SSB C-terminal tail increases the on-rate of RecQ–DNA binding and has a modest stimulatory effect on the unwinding rate of RecQ. We propose that this bidirectional communication promotes efficient DNA processing and explains how SSB stimulates rather than inhibits RecQ activity.

The palaeobiogeography of the alveolinoid Borelis species reveals the evolutionary patterns leading to the two extant representatives, which occur in shallow‐water tropical carbonate, coral reef‐related settings. Type material and new material of fossil Borelis species, along with Recent specimens were studied to assess their taxonomic status, species circumscriptions (based on proloculus size, occurrence of Y‐shaped septula, and the index of elongation), palaeobiogeography and evolutionary dynamics. The species dealt with here are known from exclusively fossil (B. pygmaea, B. inflata, B. philippinensis, B. melo, B. curdica), and from fossil and modern (B. pulchra, B. schlumbergeri) specimens. For the first time, fossil and Recent Borelis specimens are illustrated via micro‐computed tomography scanning images. Depending on the occurrence of Y‐shaped septula, two lineages are distinguished. Deriving from the middle–upper Eocene Borelis vonderschmitti, the first lineage includes B. inflata, B. pulchra and B. pygmaea, lacking Y‐shaped septula. The first species bearing Y‐shaped septula is the Rupelian B. philippinensis of the western Indo‐Pacific. The westward migrants of B. philippinensis into the Mediterranean gave rise to B. melo (Aquitanian–Messinian) and B. curdica (Burdigalian–Tortonian). These two species became isolated from the Indo‐Pacific by the Langhian eastern closure of the Mediterranean basin and disappeared during the Messinian Salinity Crisis. Since the Tortonian, B. schlumbergeri, which descended from B. philippinensis, has inhabited the Indo‐Pacific along with B. pulchra. From the central Pacific Ocean, B. pulchra reached the Caribbean area before the early Piacenzian closure of the Central America seaway.

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Chaotic Scattering in the presence of an external magnetic field Breymann, W.; Kovacs, Z.; Tel, T.