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50 years ago, Jardetzky proposed the alternating-access model, which has shaped the theoretical understanding of how substrates are carried across cell membranes. Two studies now demonstrate that transporters from distinct families undergo unexpectedly large elevator-like movements and also suggest that an 'elevate and twist' mechanism is a common means of achieving alternating access across the membrane.
During assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs), the RNA-binding protein (RBP) Gemin5 recognizes the snRNP code and interacts with the large Gemin2–SMN complex. So et al. now find that Gemin2 also interacts with U1-70K, thereby conferring a preferential advantage on U1 snRNP assembly, and they extrapolate that SMN–Gemin2 serves a general ribonucleoprotein-exchange function.
The crystal structure of the full five-subunit BAM complex from Escherichia coli reveals the interactions between individual components and domains and provides insights into the biogenesis of β-barrel outer-membrane proteins.
A combination of evolutionary covariance, biochemistry and SAXS analyses reveal that Escherichia coli FliG exists as a monomer in solution but forms domain-swapped polymers in assembled flagellar motors, thus leading to a thermodynamic model for self-assembly.
Single-molecule FRET data reveal that CENP-A alters nucleosome structure by facilitating lateral passing of the two DNA gyres; this change is reversed by the nonhistone centromere protein CENP-C.
Complementary biochemical and genetic analyses reveal that SUMOylation of the six subunits of the MCM2–7 DNA helicase inhibits CMG formation, thereby negatively regulating DNA replication initiation in budding yeast.
A 3.7- to 4.8-Å cryo-EM structure of the yeast CMG complex resolves two Mcm2–7 helicase conformations that may drive complex translocation and reveals an Mcm5-subunit domain inserted into the central channel, thus supporting a steric-exclusion model of DNA unwinding.
The higher abundance of U1 among snRNPs is explained by the identification of an additional mode of assembly: RBP U1-70K bridges pre-U1 to SMN–Gemin2–Sm, thus establishing a Gemin5-independent assembly pathway.
In addition to controlling Pol II pausing at promoters, the small nuclear RNA 7SK inhibits transcription at enhancers and super enhancers by recruiting the chromatin-remodeling complex BAF
Mapping the spatial distribution of interaction sites between FG nucleoporins and nuclear transport receptors within the native NPC through SPEED microscopy reveals the 3D configuration of the FG-nucleoporin barrier and competition among transport receptors.
New crystal structures of the NapA antiporter in both outward- and inward-facing conformations provide evidence for an elevator-like ion-translocation mechanism in sodium/proton exchangers.
‘Repeat swap’ modeling of the outward-facing conformation and biochemical analyses show that the bacterial VcINDY symporter uses an elevator-type mechanism for substrate transport across the cell membrane.
