Finding Homologs in Amino Acid Sequences Using Network BLAST Searches

Istvan Ladunga1

1 Departments of Statistics, Biochemistry and School of Biological Sciences, University of Nebraska–Lincoln, Lincoln, Nebraska
Publication Name:  Current Protocols in Bioinformatics
Unit Number:  Unit 3.4
DOI:  10.1002/cpbi.34
Online Posting Date:  September, 2017
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BLAST, the Basic Local Alignment Search Tool, is used more frequently than any other biosequence database search program. We show how to run searches on the Web, and demonstrate how to increase performance by fine‐tuning arguments for a specific research project. We offer guidance for interpreting results, statistical significance and biological relevance issues, and suggest complementary analyses. This unit covers both protein‐to‐protein (blastp) searches and translated searches (blastx, tblastn, tfastx). blastx conceptually translates the query sequence and tblastn translates all nucleotide sequences in a database, while tblastx translates both the query and the database sequences into amino acid sequences. © 2017 by John Wiley & Sons, Inc.

Keywords: BLAST; Basic Local Alignment Search Tool; Sequence similarity search; Protein function prediction; Homology; translated BLAST searches

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Table of Contents

  • Introduction
  • Basic Protocol 1: Using the Web‐Interface BLAST for BLASTP: Protein‐to‐ Protein Searches
  • Support Protocol 1: Setting Arguments (Options) for Advanced BLAST
  • Support Protocol 2: Formatting Results from a BLAST Search
  • Basic Protocol 2: Translated BLAST Searches
  • Basic Protocol 3: Comparing Two or More Sequences
  • Guidelines for Understanding Results
  • Commentary
  • Literature Cited
  • Figures
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Literature Cited

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Key References
  Altschul, S. F., Boguski, M. S., Gish, W., & Wootton, J. C. (1994). Issues in searching molecular sequence databases. Nature Genetics 6, 119‐129.
  Probably the best description of the BLAST program that produced nongapped alignments at that time. This review discusses the underlying statistics and their biological interpretation, the scoring schemes, the search, the sensitivity, and selectivity on biological examples.
  Altschul et al., 1997. See above.
  The original research paper on gapped and PSI‐BLAST. Both are significant improvements over earlier BLAST versions. Computational speed, increased sensitivity, and decreased selectivity are analyzed.
  Gish & States, 1993. See above.
  The original research paper about translated BLAST. The authors evaluate the advantages and pitfalls of this application when processing introns, frameshifts, and similar issues. Besides the theory, implications for statistical significance are illustrated using detailed examples.
Internet Resources
  The NCBI BLAST Web site.‐bin/RepeatMasker
  The RepeatMasker Web site.
  Coiled coil predictions.
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