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- Bosaeus, N., et al.
(author)
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A stretched conformation of DNA with a biological role?
- 2017
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In: Quarterly Reviews of Biophysics. - : Cambridge University Press (CUP). - 0033-5835 .- 1469-8994. ; 50
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Journal article (peer-reviewed)abstract
- We have discovered a well-defined extended conformation of double-stranded DNA, which we call Sigma-DNA, using laser-tweezers force-spectroscopy experiments. At a transition force corresponding to free energy change Delta G = 1.57 +/- 0.12 kcal (mol base pair)(-1) 60 or 122 base-pair long synthetic GC-rich sequences, when pulled by the 3'-3' strands, undergo a sharp transition to the 1.52 +/- 0.04 times longer Sigma-DNA. Intriguingly, the same degree of extension is also found in DNA complexes with recombinase proteins, such as bacterial RecA and eukaryotic Rad51. Despite vital importance to all biological organisms for survival, genome maintenance and evolution, the recombination reaction is not yet understood at atomic level. We here propose that the structural distortion represented by Sigma-DNA, which is thus physically inherent to the nucleic acid, is related to how recombination proteins mediate recognition of sequence homology and execute strand exchange. Our hypothesis is that a homogeneously stretched DNA undergoes a 'disproportionation' into an inhomogeneous Sigma-form consisting of triplets of locally B-like perpendicularly stacked bases. This structure may ensure improved fidelity of base-pair recognition and promote rejection in case of mismatch during homologous recombination reaction. Because a triplet is the length of a gene codon, we speculate that the structural physics of nucleic acids may have biased the evolution of recombinase proteins to exploit triplet base stacks and also the genetic code.
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- Sjögren, Klara, 1970, et al.
(author)
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Body fat content can be predicted in vivo in mice using a modified dual-energy X-ray absorptiometry technique.
- 2001
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In: The Journal of nutrition. - : Elsevier BV. - 0022-3166. ; 131:11, s. 2963-6
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Journal article (peer-reviewed)abstract
- The introduction of transgenic mice as animal models in medical research has increased the need for methods to study the phenotype of mice. The aim of the present study was to develop and evaluate a method for in vivo prediction of fat content in living mice. We combined a modified dual-energy X-ray technique with an image analysis procedure. This combined procedure calculates the percentage of fat area, defined as the percentage of the total area of the mice consisting of >50% fat. A high correlation between the percentage of fat area and dissected adipose tissue was seen in both male and female mice (males, r = 0.92, P < 0.001; females, r = 0.88, P < 0.001). A high correlation was also seen between the percentage of fat area and serum levels of leptin (males, r = 0.95, P < 0.001; females, r = 0.86, P < 0.001). An additional experiment demonstrated a very strong correlation between the percentage of fat area and total body fat as determined by chemical extraction (r = 0.97, P < 0.001). In summary, the percentage of fat area, as measured with the dual-energy X-ray/image combined procedure, provides a good in vivo estimation of total body fat content in mice.
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