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Bioinformatics Algorithms: Techniques and Applications

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216 INTEGER LINEAR PROGRAMMING TECHNIQUES<br />

CPU time [4 hrs]; Normalized objective function c *(D) /D<br />

0.8<br />

0.7<br />

0.6<br />

0.5<br />

0.4<br />

0.3<br />

0.2<br />

0.1<br />

CPU time [units of 4 h]<br />

Normalized objective<br />

function c * (D) /D<br />

0<br />

0 50 100 150 200 250 300 350 400 450 500<br />

Cluster size D<br />

FIGURE 9.2 Comparison of C. glutamicum <strong>and</strong> M. tuberculosis: For each cluster size D ∈<br />

[5,500], the running time in units of 4 h, <strong>and</strong> the normalized optimal value of the objective<br />

function is shown. Note the local minima in the objective function, for example, at D = 51.<br />

The apparent correlation between objective function <strong>and</strong> running time indicates that good<br />

approximate clusters are easier to compute than bad clusters.<br />

9.5.3 A 28-Cluster in a 20-Genome Set<br />

We attempt to find a large approximate gene cluster in several genomes. We thank<br />

Thomas Schmidt (Bielefeld) for providing a dataset of the following twenty bacterial<br />

genomes (number of genes given in brackets): B. longum (1727), B. subtilis (4103),<br />

C. diphtheriae (2272), C. efficiens (2942), C. glutamicum (3057), E. coli K12 (4288),<br />

L. lactis (2266), L. xyli (2030), M. avium (4350), M. leprae (1605), M. tuberculosis<br />

(3991), N. farcinica (5683), P. acnes (2297), P. aeruginosa (5566), P. putida (5350),<br />

S. avermitilis (7575), S. coelicolor (7768), S. thermophilum (3337), T. whipplei (808),<br />

<strong>and</strong> W. succinogenes (2044).<br />

FIGURE 9.3 Visualization of an interesting optimal cluster in C. glutamicum <strong>and</strong> M. tuberculosis<br />

(D = 51). Differing genes are marked in gray. Three conserved regions, a, b, <strong>and</strong> c<br />

occur in the cluster.

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