How does PSI-BLAST work?

• A single database search might locate some sequences that are related to the query sequence. Information from these related sequences can then be used in further searches to locate yet more related sequences.

• Essentially we are using intermediate sequences to infer similarity between two sequences that are too dissimilar to link directly.

• When using PSI-BLAST the results of a normal BLAST search are aligned and used to construct a pattern of conserved residues. This pattern is used for the next round of searching instead of the original query sequence.

• The process is repeated (iterated) until a final database search finds no more related sequences. When the process ends in this fashion, it is said to have converged.

Move on to the tutorial on how to use PSI-BLAST

Back to section 2