PrrC-anticodon nuclease: functional organization of a prototypical bacterial restriction RNase

The tRNA(Lys) anticodon nuclease PrrC is associated in latent form with the type Ic DNA restriction endonuclease EcoprrI and activated by a phage T4-encoded inhibitor of EcoprrI. The activation also requires the hydrolysis of GTP and presence of dTTP and is inhibited by ATP. The N-proximal NTPase domain of PrrC has been implicated in relaying the activating signal to a C-proximal anticodon nuclease site by interacting with the requisite nucleotide cofactors [Amitsur et al. (2003) Mol. Microbiol., 50, 129–143]. Means described here to bypass PrrC's self-limiting translation and thermal instability allowed purifying an active mutant form of the protein, demonstrating its oligomeric structure and confirming its anticipated interactions with the nucleotide cofactors of the activation reaction. Mutagenesis and chemical rescue data shown implicate the C-proximal Arg(320), Glu(324) and, possibly, His(356) in anticodon nuclease catalysis. This triad exists in all the known PrrC homologs but only some of them feature residues needed for tRNA(Lys) recognition by the Escherichia coli prototype. The differential conservation and consistent genetic linkage of the PrrC proteins with EcoprrI homologs portray them as a family of restriction RNases of diverse substrate specificities that are mobilized when an associated DNA restriction nuclease is compromised

Rodent phylogeny revised: analysis of six nuclear genes from all major rodent clades

<p>Abstract</p> <p>Background</p> <p>Rodentia is the most diverse order of placental mammals, with extant rodent species representing about half of all placental diversity. In spite of many morphological and molecular studies, the family-level relationships among rodents and the location of the rodent root are still debated. Although various datasets have already been analyzed to solve rodent phylogeny at the family level, these are difficult to combine because they involve different taxa and genes.</p> <p>Results</p> <p>We present here the largest protein-coding dataset used to study rodent relationships. It comprises six nuclear genes, 41 rodent species, and eight outgroups. Our phylogenetic reconstructions strongly support the division of Rodentia into three clades: (1) a "squirrel-related clade", (2) a "mouse-related clade", and (3) Ctenohystrica. Almost all evolutionary relationships within these clades are also highly supported. The primary remaining uncertainty is the position of the root. The application of various models and techniques aimed to remove non-phylogenetic signal was unable to solve the basal rodent trifurcation.</p> <p>Conclusion</p> <p>Sequencing and analyzing a large sequence dataset enabled us to resolve most of the evolutionary relationships among Rodentia. Our findings suggest that the uncertainty regarding the position of the rodent root reflects the rapid rodent radiation that occurred in the Paleocene rather than the presence of conflicting phylogenetic and non-phylogenetic signals in the dataset.</p

Parallel dimerization of a PrrC-anticodon nuclease region implicated in tRNALys recognition

The optional Escherichia coli restriction tRNase PrrC represents a family of potential antiviral devices widespread among bacteria. PrrC comprises a functional C-domain of unknown structure and regulatory ABC/ATPase-like N-domain. The possible involvement of a C-domain sequence in tRNALys recognition was investigated using a matching end-protected 11-meric peptide. This mimic, termed here LARP (Lys-anticodon recognizing peptide) UV-cross-linked tRNALys anticodon stem-loop (ASL) analogs and inhibited their PrrC-catalyzed cleavage. Trimming LARP or introducing in it inactivating PrrC missense mutations impaired these activities. LARP appeared to mimic its matching protein sequence in ability to dimerize in parallel, as inferred from the following results. First, tethering Cys to the amino- or carboxy-end of LARP dramatically enhanced the ASL-cross-linking and PrrC-inhibiting activities under suitable redox conditions. Second, Cys-substitutions in a C-domain region containing the sequence corresponding to LARP elicited specific intersubunit cross-links. The parallel dimerization of PrrC's C-domains and expected head-to-tail dimerization of its N-domains further suggest that the NTPase and tRNALys-binding sites of PrrC arise during distinct assembly stages of its dimer of dimers form

Physiological expression of mutated TAU impaired astrocyte activity and exacerbates β-amyloid pathology in 5xFAD mice

Abstract Background Alzheimer’s disease (AD) is the leading cause of dementia in the world. The pathology of AD is affiliated with the elevation of both tau (τ) and β-amyloid (Aβ) pathologies. Yet, the direct link between natural τ expression on glia cell activity and Aβ remains unclear. While experiments in mouse models suggest that an increase in Aβ exacerbates τ pathology when expressed under a neuronal promoter, brain pathology from AD patients suggests an appearance of τ pathology in regions without Aβ. Methods Here, we aimed to assess the link between τ and Aβ using a new mouse model that was generated by crossing a mouse model that expresses two human mutations of the human MAPT under a mouse Tau natural promoter with 5xFAD mice that express human mutated APP and PS1 in neurons. Results The new mouse model, called 5xFAD TAU, shows accelerated cognitive impairment at 2 months of age, increased number of Aβ depositions at 4 months and neuritic plaques at 6 months of age. An expression of human mutated TAU in astrocytes leads to a dystrophic appearance and reduces their ability to engulf Aβ, which leads to an increased brain Aβ load. Astrocytes expressing mutated human TAU showed an impairment in the expression of vascular endothelial growth factor (VEGF) that has previously been suggested to play an important role in supporting neurons. Conclusions Our results suggest the role of τ in exacerbating Aβ pathology in addition to pointing out the potential role of astrocytes in disease progression. Further research of the crosstalk between τ and Aβ in astrocytes may increase our understanding of the role glia cells have in the pathology of AD with the aim of identifying novel therapeutic interventions to an otherwise currently incurable disease