Abstract
We have implemented a novel gapped-alignment algorithm to compare Position Frequency Matrices (PFMs) for Transcription Factor Binding Sites. The application compares an input PFM with those collected from public databases and outputs similarity scores, sequence alignments and related PFM clusters. MACO is freely accessible on a web server located at www.nicemice.cn/bioinfo/MACO. Source code is distributed upon request to the authors.