Non-approximability of Weighted Multiple Sequence Alignment

  • Authors:
  • Bodo Siebert

  • Affiliations:
  • -

  • Venue:
  • COCOON '01 Proceedings of the 7th Annual International Conference on Computing and Combinatorics
  • Year:
  • 2001

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Abstract

We consider a weighted generalization of multiple sequence alignment with sum-of-pair score. Multiple sequence alignment without weights is known to be NP-complete and can be approximated within a constant factor, but it is unknown whether it has a polynomial time approximation scheme. Weighted multiple sequence alignment can be approximated within a factor of O(log2 n) where n is the number of sequences. We prove that weighted multiple sequence alignment is MAX SNP-hard and establish a numerical lower bound on its approximability, namely 324/323 - ε. This lower bound is obtained already for the simple binary weighted case where the weights are restricted to 0 and 1. Furthermore, we show that weighted multiple sequence alignment and its restriction to binary weights can be approximated exactly to the same degree.