How Did BLAST Work? Query Parsing for Protein-Protein Searches
(using blastp as an example algorithm)
- parse protein sequences into 3 letter "words"
- do the same for every sequence in the query database
- identify database sequences with word matches that have a certain minimum ("threshhold") score
- extend the sequence comparison between your query and the hit in both directions
- report the hit in the search results if it meets or exceeds the BLAST cutoffs for a statistically significant match
Sources: image from the BLAST Tutorial, accessible from NCBI's
Education web page.
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