GATE 2023 BT – Question 26
Which one of the following programs is used for finding distantly related (or remote) protein homologs?
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Correct answer: (C) PSI-BLAST
Explanation
Remote homologs share little sequence identity, so a simple pairwise search with one query sequence misses them.
- **BLASTN:** nucleotide against nucleotide.
- **BLASTX:** translated nucleotide query against a protein database.
- **TBLASTX:** translated query against a translated nucleotide database.
- **PSI-BLAST (Position-Specific Iterated BLAST):** runs a BLASTP search, builds a position-specific scoring matrix (a profile) from the significant hits, and searches again with that profile. Each iteration adds more distant relatives, so it finds **remote protein homologs**. ✓
Answer **PSI-BLAST** (C).