BIOPHYSICAL THEORY AND MODELING |
Numerical investigation of sequence dependence in homologous recognition : evidence for homology traps
Renaud Fulconis 1*, Marie Dutreix 2 and Jean-Louis Viovy 1
1 Institut Curie, UMR CNRS 168
2 Institut Curie, UMR CNRS 2027
* To whom correspondence should be addressed. E-mail: renaud.fulconis{at}polytechnique.org.
Submitted on October 28, 2004
Revised on January 18, 2005
Accepted on 2 March 2005
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Abstract |
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During the initial phase of RecA-mediated recombination, known as the search for homology, a single-stranded DNA coated by RecA protein and a homologous double-stranded DNA have to perfectly align and pair. We designed a model for the homology search between short molecules, and performed Monte-Carlo Metropolis computer simulations of the process. The central features of our model are : the assumption that duplex DNA longitudinal thermal fluctuations are instrumental in the binding ; and the explicit consideration of the nucleotide sequence. According to our results, recognition undergoes a first slow nucleation step over a few base pairs, followed by a quick extension of the pairing to adjacent bases. The formation of the three-stranded complex tends to be curbed by heterologies but also by another possible obstacle : the presence of partially homologous stretches, such as mono- or polynucleotide repeats. Actually, repeated sequences are observed to trap the molecules in unproductive configurations. We investigate the dependence of the phenomenon on various energy parameters. This mechanism of homology trapping could have a strong biological relevance in the light of the genomic instability experimentally known to be triggered by repeated sequences.
Key Words:
DNA, Monte-Carlo Metropolis, RecA, homologous pairing, repeated sequences, substitutions
