A simple and space-efficient fragment-chaining algorithm for alignment of DNA and protein sequences

In the segment-based approach to sequence alignment, nucleic acid, and prot ein sequence alignments are constructed from fragments, i.e., from pairs of ungapped segments of the input sequences. Given a set F of candidate fragm ents and a weighting function w : F --> R-0(+), the score of an alignment i s defined as the sum of weights of the fragments it consists of, and the op timization problem is to find a consistent collection of pairwise disjoint fragments with maximum sum of weights. Herein, a sparse dynamic programming algorithm is described that solves the pairwise segment-alignment problem in O(L + N-max) space where L is the maximum length of the input sequences while N-max less than or equal to #F holds. With a recently introduced weig hting function w, small sets F of candidate fragments are sufficient to obt ain alignments of high quality, As a result, the proposed algorithm runs in essentially linear space. (C) 2001 Elsevier Science Ltd. All rights reserv ed.