Using BLAST for performing sequence alignment.

BLAST is a widely used genetic sequence comparison program developed at the National Center for Biotechnology Information (NCBI). In this unit, three Basic Protocols and one Support Protocol are provided for general-purpose BLAST searches on the NCBI and ENSEMBL Web-accessible BLAST servers. Key parameters affecting how the search algorithm works are reviewed, with advice on modifying search parameters for specific situations. Many other public and private Web sites offer BLAST interfaces which may differ from those described in this unit, but the general principles will be similar. The Support Protocol describes how to obtain sequences in various formats from NCBI for use in BLAST searches. It is emphasized that no algorithm can be a substitute for biological understanding; performing a BLAST search takes only a few minutes but understanding the implications of the results takes much longer.