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Two proposed mechanisms for how microRNAs (miRNAs) and their associated Argonaute proteins inhibit translation in mammals do not seem to operate in Drosophila melanogaster cells, suggesting that insights into important miRNA functions remain elusive. However, the interaction between Argonaute and the P-body factor GW182 may help in elucidating the biochemical basis of translational control by miRNAs.
The ankyrin repeats of the G9a and GLP histone methyltransferases have now been shown to be binding modules for mono- and dimethyllysine histone H3 lysine 9 (H3K9), revealing a new function for an ankyrin repeat domain and showing that a polypeptide chain can both create and recognize the same histone mark.
Assembly of the 34-subunit, 2.5 megadalton 26S proteasome starts with formation of the seven-membered α-ring. A set of newly identified proteasome chaperones serves as a clamp to seal α-rings with the correct composition. By regulating the efficiency and outcome of this crucial step in proteasome biogenesis, these dedicated proteasome chaperones apparently partake in the stress response and in adaptation to intracellular proteolysis needs.
The compositional complexity of the spliceosome creates a serious obstacle for its experimental analysis. Purification of a compositionally defined splicing complex C capable of completing the second step of splicing in the absence of additional proteins opens the door for future mechanistic and structural analyses.
The kinase regulatory-loop binding (KRLB) region of insulin receptor substrate 2 was originally thought to be a new type of domain with binding properties similar to phosphotyrosine binding (PTB) domains. A crystallographic study now shows that KRLB is actually a short peptide segment that binds to the insulin receptor using an extended series of contacts that mimic both autoinhibitory loop and ATP binding to its catalytic cleft.
An immense range of polysaccharide structures is expressed on the bacterial surface. The length of the polymer can be a crucial attribute for virulence. Members of a family of 'polysaccharide copolymerase' proteins are essential for the regulation of polymer chain length, participating in one widespread biosynthesis scheme.
Transient mechanical stresses induced by molecular motors that move DNA can propagate through the chromatin fiber and trigger local DNA alterations that in turn allow for specific DNA-protein interactions. Hence, DNA supercoiling modulations and chromatin conformational dynamics concur in gene regulation.
Bacterial type III secretion machines have adapted to carry out numerous functions, ranging from locomotion to protein delivery into nucleated cells. One of the most intriguing issues is the source of energy that fuels their activities. Despite recent advances, there are still many questions to be resolved.
Structural biology is making significant contributions toward an understanding of molecular constituents and mechanisms underlying human diseases at an atomic resolution, as discussed at the international Murnau Conference on Structural Biology of Disease Mechanisms held in September 2007 in Murnau, Germany.
Circadian rhythms are generated by cell-autonomous molecular clocks in organisms ranging from cyanobacteria to humans. Recent research on the mechanisms of molecular clocks call for a reflection on the cause and necessity of complexity in biological systems.
DNA damage activates signaling cascades driven by the ATM–ATR protein kinases, culminating in the recruitment of repair proteins to the damage site through poorly understood mechanisms. Now a flurry of papers reveals how ATM-dependent phosphorylation of mediator and chromatin-associated proteins at sites of double-strand breaks promotes ubiquitylation of local nucleosomes, thereby eliciting a powerful signal for recruitment of repair complexes to the damage site.
