Contextual PSI-BLAST Project |
CTX-PSI-BLAST is an extension of NCBI Toolkit that incorporates contextual alignment model [3,4] into the iterative version of BLAST algorithm known as PSI-BLAST [1]. It allows to investigate the effect of context-dependency in the protein alignment in genomic scale. The software makes use of non-symmetric contextual substitution tables and calculates the statistical significance of a given alignment according to the contextual statistical model.
The version of NCBI Toolkit used to implement contextual extension was Mar_17_2008. It is available at the NCBI FTP site.
The source code was compiled under Linux PLD with GCC 4.4.1 and it is suggested to use GCC in version 4.4.1 at least. The list of all modified files can be found in the readme.txt file contained in the distribution.
To build an application run the following in the project root directory:
CTX-PSI-BLAST executable file (psiblast) can be found in GCC{version}-Release/bin.
The following command runs the standard version of PSI-BLAST:
where
The contextual version of PSI-BLAST requires two additional parameters:
[1] S.F. Altschul, T.L. Madden, A.A. Schaffer, J. Zhang, Z. Zhang, W. Miller, and D.J.
Lipman. Gapped BLAST and PSI-BLAST: a new generation of protein database search
programs. Nucleic Acids Research, 25:3389-3402, 1997.
[2] I. Friedberg, T. Kaplan, and H. Margalit. Evaluation of PSI-BLAST alignment accuracy
in comparison to structural alignments. Protein Science, Cambridge University
Press, 9:2278-2284, 2000.
[3] A. Gambin and J. Tyszkiewicz. Substitution matrices for contextual alignment.
Journees Ouvertes Biologie Informatique Mathematique, J. Nicolas and C. Thermes (eds.),
227-238, 2002.
[4] A. Gambin, S. Lasota, R. Szklarczyk, J. Tiuryn, and J. Tyszkiewicz. Contextual
Alignment of Biological Sequences. Proc. ECCB 02, Bioinformatics, Oxford University
Press, 18:116-127, 2002.
All source code can be downloaded from here.
ab209455[at]students.mimuw.edu.pl