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Internal ribosomal entry sites help initiate translation of some viral transcripts. Kieft and colleagues present the structure of a Dicistroviridae IRES domain. Its structural mimicry of the host tRNA-mRNA interaction suggests how this RNA is able to kick start translation alone. This molecular mimicry is represented by organismal mimicry in the cover photograph by Ra'id Khalil, from istockphoto.com.pp 57-64
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.
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.