This BLAST information guide is designed to assist new and veteran users in employing NCBI tools such as BLAST and PSI-BLAST in their research. The three tutorials (Query, BLAST and PSI-BLAST) offer starting points for users with different backgrounds. A novice should start with the Query tutorial. More experienced users will want to work through the BLAST tutorial before proceeding to the more advanced PSI-BLAST tutorial.

Sequence alignments provide a powerful way to compare novel sequences with previously characterized genes. Both functional and evolutionary information can be inferred from well designed queries and alignments. BLAST 2.0, (Basic Local Alignment Search Tool), provides a method for rapid searching of nucleotide and protein databases. Since the BLAST algorithm detects local as well as global alignments, regions of similarity embedded in otherwise unrelated proteins can be detected. Both types of similarity may provide important clues to the function of uncharacterized proteins.