SIMILARITY DETECTION AND LOCALIZATION

The detection of similarities between long DNA and protein sequences i s studied using concepts of statistical physics. It is shown that mutu al similarities can be detected by sequence alignment methods only if their amount exceeds a threshold value. The onset of detection is a cr itical phase transition viewed as a localization-delocalization transi tion. The fidelity of the alignment is the order parameter of that tra nsition; it leads to criteria to select optimal alignment parameters.