In eukaryotes, supercoiling generated by transcription is implicated in the regulation of oncogenes such as c-Myc 7. Supercoiling operates synergistically with nuclear-associated proteins to regulate bacterial gene expression 6. In prokaryotes, genomic DNA has an average density of supercoiling, σ (∆Lk/original Lk) of ~−0.06 5. The conformational response to this stress is called negative supercoiling, partitioned between untwisting of the helix (change in twist Tw) and a coiling deformation of the DNA backbone (writhe Wr) 1, 2, 3, 4. Negative superhelical stress results from a reduction in the number of links (Lk) between the two strands of a closed-circular DNA (a negative ∆Lk). Genomic DNA is often subjected to torsional stress, which can both over- and under-wind the DNA double helix 1, 2, 3. Our results provide mechanistic insight into how DNA supercoiling can affect molecular recognition, that may have broader implications for DNA interactions with other molecular species. We show that the energetics of triplex formation is governed by a delicate balance between electrostatics and bonding interactions. We probe how these local and global conformational changes affect DNA interactions through the binding of triplex-forming oligonucleotides to DNA minicircles. We observe that negative superhelical stress induces local variation in the canonical B-form DNA structure by introducing kinks and defects that affect global minicircle structure and flexibility. Here, we overcome these limitations, by a combination of atomic force microscopy (AFM) and atomistic molecular dynamics (MD) simulations, to resolve structures of negatively-supercoiled DNA minicircles at base-pair resolution. It remains unclear how this supercoiling affects the detailed double-helical structure of DNA, largely because of limitations in spatial resolution of the available biophysical tools.
Read on to learn the horrific truth of these sinister rodents you voluntarily welcome into your home.In the cell, DNA is arranged into highly-organised and topologically-constrained (supercoiled) structures. Hamsters, it turns out, are blind, alcoholic, inbred, murderous, cannibalistic cranks. But underneath that cute exterior lies a miserable pile of dark secrets. The Chinese hamster is less common as a pet, partially because of the male's large and conspicuous genitals, which can grow to be as large as their head.Įnormous business notwithstanding, hamsters are famed for being cute little balls of fuzz who just run on their wheels or in their plastic balls and lap beads of water out of their little water bottles and dig around in wood chips and what have you. Various species of dwarf hamster are also common as pets, including the Roborovski hamster, known colloquially as the Robo, despite not being a cool cybernetic hamster of the future.
The most common domestic hamster by far is the Syrian or golden hamster, also called the fancy hamster, if you want to gild the lily a little. Hamsters are incredibly popular pets, especially as "starter pets" for kids whose parents don't feel they're ready for the responsibility of a larger, more difficult pet that would cause more of an uproar with the neighbors if the kid does a bad job taking care of it.
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