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A stretched conformation of DNA with a biological role?

Niklas Bosaeus (Institutionen för biologi och bioteknik, Kemisk biologi) ; A. Reymer ; T. Beke-Somfai ; T. Brown ; M. Takahashi ; Pernilla Wittung-Stafshede (Institutionen för biologi och bioteknik, Kemisk biologi) ; Sandra Rocha (Institutionen för biologi och bioteknik, Kemisk biologi) ; Bengt Nordén (Institutionen för kemi och kemiteknik, Fysikalisk kemi)
Quarterly Reviews of Biophysics (0033-5835). Vol. 50 (2017), p. UNSP e11.
[Artikel, refereegranskad vetenskaplig]

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.



Denna post skapades 2017-08-30.
CPL Pubid: 251524

 

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