On the Complexity of Constrained Sequences Alignment Problems

Abstract

We consider the problem of aligning a set of sequences subject to a given constrained sequence, which has applications in computational biology. In this paper we show that sequence alignment for two sequences A and B with a given distance function and a constrained sequence of k identical characters (say character c) can be solved in O( min {kn 2,(t − k)n 2}) time, where n is the length of A and B, and t is the minimum number of occurrences of character c in A and B. We also prove that the problem of constrained center-star sequence alignment (CCSA) is NP-hard even over the binary alphabet. Furthermore, for some distance function, we show that no polynomial-time algorithm can approximate the CCSA within any constant ratio.