Impact of the energy model on the complexity of RNA folding with pseudoknots

  • Authors:
  • Saad Sheikh;Rolf Backofen;Yann Ponty

  • Affiliations:
  • University of Florida, Gainesville, USA,AMIB Team-Project, INRIA, Saclay, France;Albert Ludwigs University, Freiburg, Germany;Ecole Polytechnique, CNRS UMR 7161, Palaiseau, France,AMIB Team-Project, INRIA, Saclay, France

  • Venue:
  • CPM'12 Proceedings of the 23rd Annual conference on Combinatorial Pattern Matching
  • Year:
  • 2012

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Abstract

Predicting the folding of an RNA sequence, while allowing general pseudoknots (PK), consists in finding a minimal free-energy matching of its n positions. Assuming independently contributing base-pairs, the problem can be solved in Θ(n3)-time using a variant of the maximal weighted matching. By contrast, the problem was previously proven NP-Hard in the more realistic nearest-neighbor energy model. In this work, we consider an intermediate model, called the stacking-pairs energy model. We extend a result by Lyngsø, showing that RNA folding with PK is NP-Hard within a large class of parametrization for the model. We also show the approximability of the problem, by giving a practical Θ(n3) algorithm that achieves at least a 5-approximation for any parametrization of the stacking model. This contrasts nicely with the nearest-neighbor version of the problem, which we prove cannot be approximated within any positive ratio, unless P=NP.