An Efficient Algorithm for String Motif Discovery

Finding common patterns, motifs, in a set of DNA sequences is an important problem in bioinformatics. One common representation of motifs is a string with symbols A, C, G, T and N where N stands for the wildcard symbol. In this paper, we introduce a more general motif discovery problem without any weaknesses of the Planted (l,d)-Motif Problem and also a set of control sequences as an additional input. The existing algorithms using brute force approach for solving similar problem take O(n(t+f)l5) times where t and f are the number of input sequences and control sequences respectively, n is the length of each sequence and l is the length of the motif. We propose an efficient algorithm, called VAS, which has an expected running time O(nfl(nt)(4+1/4)) using O((nt)(4+1/4)) space for any integer k. In particular when k = 3, the time and space complexities are O(nlf (nt)(1.0625)) and O((nt)(1.0625)) respectively. This algorithm makes use of voting and graph representation for better time and space complexities. This technique can also be used to improve the performances of some existing algorithms.