A novel physiological role for ARF1 in the formation of bidirectional tubules from the Golgi.

Capitalizing on CRISPR/Cas9 gene-editing techniques and super-resolution nanoscopy, we explore the role of the small GTPase ARF1 in mediating transport steps at the Golgi. Besides its well-established role in generating COPI vesicles, we find that ARF1 is also involved in the formation of long (∼3 µm), thin (∼110 nm diameter) tubular carriers. The anterograde and retrograde tubular carriers are both largely free of the classical Golgi coat proteins coatomer (COPI) and clathrin. Instead, they contain ARF1 along their entire length at a density estimated to be in the range of close packing. Experiments using a mutant form of ARF1 affecting GTP hydrolysis suggest that ARF1[GTP] is functionally required for the tubules to form. Dynamic confocal and stimulated emission depletion imaging shows that ARF1-rich tubular compartments fall into two distinct classes containing 1) anterograde cargoes and clathrin clusters or 2) retrograde cargoes and coatomer clusters

Two-colour live-cell nanoscale imaging of intracellular targets.

Stimulated emission depletion (STED) nanoscopy allows observations of subcellular dynamics at the nanoscale. Applications have, however, been severely limited by the lack of a versatile STED-compatible two-colour labelling strategy for intracellular targets in living cells. Here we demonstrate a universal labelling method based on the organic, membrane-permeable dyes SiR and ATTO590 as Halo and SNAP substrates. SiR and ATTO590 constitute the first suitable dye pair for two-colour STED imaging in living cells below 50 nm resolution. We show applications with mitochondria, endoplasmic reticulum, plasma membrane and Golgi-localized proteins, and demonstrate continuous acquisition for up to 3 min at 2-s time resolution

The genetic prehistory of southern Africa

Southern and eastern African populations that speak non-Bantu languages with click consonants are known to harbour some of the most ancient genetic lineages in humans, but their relationships are poorly understood. Here, we report data from 23 populations analyzed at over half a million single nucleotide polymorphisms, using a genome-wide array designed for studying human history. The southern African Khoisan fall into two genetic groups, loosely corresponding to the northwestern and southeastern Kalahari, which we show separated within the last 30,000 years. We find that all individuals derive at least a few percent of their genomes from admixture with non-Khoisan populations that began approximately 1,200 years ago. In addition, the east African Hadza and Sandawe derive a fraction of their ancestry from admixture with a population related to the Khoisan, supporting the hypothesis of an ancient link between southern and eastern AfricaComment: To appear in Nature Communication

Suppression of p53 response by targeting p53-Mediator binding with a stapled peptide

DNA-binding transcription factors (TFs) remain challenging to target with molecular probes. Many TFs function in part through interaction with Mediator, a 26-subunit complex that controls RNA polymerase II activity genome-wide. We sought to block p53 function by disrupting the p53-Mediator interaction. Through rational design and activity-based screening, we characterize a stapled peptide, with functional mimics of both p53 activation domains, that blocks p53-Mediator binding and selectively inhibits p53-dependent transcription in human cells; importantly, this &ldquo;bivalent&rdquo; peptide has negligible impact, genome-wide, on non-p53 target genes. Our proof-of-concept strategy circumvents the TF entirely and targets the TF-Mediator interface instead, with desired functional outcomes (i.e., selective inhibition of p53 activation). Furthermore, these results demonstrate that TF activation domains represent viable starting points for Mediator-targeting molecular probes, as an alternative to large compound libraries. Different TFs bind Mediator through different subunits, suggesting this strategy could be broadly applied to selectively alter gene expression programs. &nbsp;</p

In Silico Improvement of beta(3)-Peptide Inhibitors of p53 center dot hDM2 and p53 center dot hDMX

There is great interest in molecules capable of inhibiting the interactions between p53 and its negative regulators hDM2 and hDMX, as these molecules have validated potential against cancers in which one or both oncoproteins are overexpressed. We reported previously that appropriately substituted β(3)-peptides inhibit these interactions and, more recently, that minimally cationic β(3)-peptides are sufficiently cell permeable to upregulate p53-dependent genes in live cells. These observations, coupled with the known stability of β-peptides in a cellular environment, and the recently reported structures of hDM2 and hDMX, motivated us to exploit computational modeling to identify β-peptides with improved potency and/or selectivity. This exercise successfully identified a new β(3)-peptide, β53-16, that possesses the highly desirable attribute of high affinity for both hDM2 as well as hDMX and identifies the 3,4-dichlorophenyl moiety as a novel determinant of hDMX affinity. [Image: see text

Mapping RNA Regions in Eukaryotic Ribosomes That Are Accessible to Methidiumpropyl-EDTA•Fe(II) and EDTA•Fe(II)

Methidiumpropyl-EDTA•Fe(II) [MPE.Fe(II)] and EDTA•Fe(II) were used to investigate the structure of Drosophila melanogaster ribosomes. Cleavage reactions were performed on intact ribosomes in cell lysates in vitro and analyzed by primer extension with reverse transcriptase using oligodeoxynucleotide primers. Regions of 18S and 28S ribosomal RNAs (rRNAs) which are accessible to MPE•Fe(II) and EDTA•Fe(II) are located almost exclusively within expansion segments. The accessibility of these regions to cleavage indicates that they are likely exposed on the surface of eukaryotic ribosomes. These results provide information about the overall tertiary structure of rRNA in ribosomes