#
Occurrence Probability of Structured Motifs in Random Sequences,

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Robin, S., Daudin, J.-J., Richard, H., Sagot, M.-F. and Schbath, S.,

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*Submitted*.

**Abstract**

Let
he problem of extracting from a set of nucleic acid sequences
motifs which may have biological function is more and more
important. In this paper, we are interested in particular motifs
that may be implicated in the transcription process. These motifs,
called structured motifs, are composed of two ordered parts
separated by a variable distance and allowing for substitutions. In
order to assess their statistical significance, we propose
approximations of the probability of occurrence of such a structured
motif in a given sequence. An application of our method to evaluate
candidate promoters in *E. coli* and *B. subtilis* is
presented. Simulations show the goodness of the approximations.

**Key words and phrases**
Markov models, motif occurrences, promoters, structured
motifs.