E. coli RNase I exhibits a strong Ca2+-dependent inherent double-stranded RNase activity

Since its initial characterization, Escherichia coli RNase I has been described as a single-strand specific RNA endonuclease that cleaves its substrate in a largely sequence independent manner. Here, we describe a strong calcium (Ca²⁺)-dependent activity of RNase I on double-stranded RNA (dsRNA), and a Ca²⁺-dependent novel hybridase activity, digesting the RNA strand in a DNA:RNA hybrid. Surprisingly, Ca²⁺ does not affect the activity of RNase I on single stranded RNA (ssRNA), suggesting a specific role for Ca²⁺ in the modulation of RNase I activity. Mutation of a previously overlooked Ca²⁺ binding site on RNase I resulted in a gain-of-function enzyme that is highly active on dsRNA and could no longer be stimulated by the metal. In summary, our data imply that native RNase I contains a bound Ca²⁺, allowing it to target both single- and double-stranded RNAs, thus having a broader substrate specificity than originally proposed for this traditional enzyme. In addition, the finding that the dsRNase activity, and not the ssRNase activity, is associated with the Ca²⁺-dependency of RNase I may be useful as a tool in applied molecular biology.     

Flightless scaly‐tailed squirrels never learned how to fly: A reappraisal of Anomaluridae phylogeny

Anomaluroidea, commonly known as the “scaly‐tailed squirrels,” are an emblematic group of tropical African mammals that includes gliding forms. The family Anomaluridae was until recently represented by three genera: the flying scaly‐tailed squirrels (Anomalurus), the flying mouse (Idiurus) and the flightless scaly‐tailed squirrels (Zenkerella). Idiurus and Zenkerella have long been grouped into the Zenkerellinae subfamily, and Zenkerella was interpreted as a rare case of evolutionary reversal to non‐gliding lifestyle. Recent studies have demonstrated that Zenkerella is sister to all other modern anomalurids, and represents in fact the monogeneric family Zenkerellidae. The Anomalurus genus was split into Anomalurus and Anomalurops, but no study has ever considered all Anomalurus species together in a phylogeny to test the status of Anomalurops. Here, we used mitogenomic next‐generation sequencing to infer the phylogenetic relationships among all extant anomalurids and to estimate their divergence ages. We found that the arboreal Zenkerella is the sister group of all extant gliding anomalurids (Idiurus and Anomalurus). We confirmed that Anomaluroidea only evolved the gliding adaptation once. A comparison based on morphological traits indicates that Zenkerella harbours several unique morphological features. We propose new morphological characters for the novel classification of modern Anomaluroidea, which includes the families Zenkerellidae and Anomaluridae. Using different calibration schemes, we demonstrated that classical dating methods relying only on mitogenomes provide rather young Miocene estimates between Zenkerellidae and the Anomaluridae. The use of published nuclear genes, internal calibrations and tip dating converged towards an Eocene split between gliding and non‐gliding scaly‐tailed squirrels, which is in agreement with the African fossil record. Finally, we provide the first exhaustive species‐level molecular phylogenetic inference for the genus Anomalurus. We found that Anomalurus beecrofti is the sister group of all other species of Anomalurus and branched off during the Miocene.     

Assessing the reliability of an automated method for measuring dominance hierarchy in non-human primates

Primates - Among animal societies, dominance is an important social factor that influences inter-individual relationships. However, assessing dominance hierarchy can be a time-consuming activity...     

Modeling and resistant alleles explain the selectivity of antimalarial compound 49c towards apicomplexan aspartyl proteases

Toxoplasma gondii aspartyl protease 3 (TgASP3) phylogenetically clusters with Plasmodium falciparum Plasmepsins IX and X (PfPMIX, PfPMX). These proteases are essential for parasite survival, acting as key maturases for secreted proteins implicated in invasion and egress. A potent antimalarial peptidomimetic inhibitor (49c) originally developed against Plasmepsin II selectively targets TgASP3, PfPMIX, and PfPMX. To unravel the molecular basis for the selectivity of 49c, we constructed homology models of PfPMIX, PfPMX, and TgASP3 that were first validated by identifying the determinants of microneme and rhoptry substrate recognition. The flap and flap‐like structures of several reported Plasmepsins are highly flexible and critically modulate the access to the binding cavity. Molecular docking of 49c to TgASP3, PfPMIX, and PfPMX models predicted that the conserved phenylalanine residues in the flap, F344, F291, and F305, respectively, account for the sensitivity toward 49c. Concordantly, phenylalanine mutations in the flap of the three proteases increase twofold to 15‐fold the IC₅₀ values of 49c. Compellingly the selection of mutagenized T. gondii resistant strains to 49c reproducibly converted F344 to a cysteine residue.     

Octapeptide analogues of somatostatin inhibit the clonal growth and vasoactive intestinal peptide-stimulated cyclic AMP formation in human small cell lung cancer cells.

Two endocrinologically active octapeptide analogues (BIM-23014 C and BIM-23034) of somatostatin (SRIF) containing either an N- or C-terminal 3-(2-naphthyl)-D-Ala residue were examined for their ability to inhibit the in vitro receptor binding, clonal growth, and vasoactive intestinal peptide (VIP)-stimulated cyclic AMP formation in human small cell lung cancer cell (SCLC) line NCI-H345. Both SRIF peptides inhibited [125I]SRIF(Tyr11)-14 binding with IC50 values in the low nM range. Colony formation in the in vitro SCLC growth assay was also inhibited in the same concentration range, as was VIP-stimulated cyclic AMP formation. Therefore, octapeptide analogues of SRIF function as SCLC SRIF receptor agonists.     

Possible involvement of the yeast POLIII DNA polymerase in induced gene conversion

Summary In Saccharomyces cerevisiae, three different DNA polymerase complexes, POLI, POLII and POLIII, are known to be involved in DNA replication. The catalytic subunit of POLIII is encoded by the essential CDC2 gene. The existence of different thermosensitive non-complementing mutants of CDC2 offers the possibility of using a genetic approach to investigate the involvement of POLIII in induced gene conversion. When cdc2 heteroallelic cells were irradiated and incubated under restrictive conditions, almost no induction of thermoresistant cells could be detected, suggesting an essential role for POLIII in mitotic gene conversion events.