compares an amino acid query sequence against a protein sequence
database
blastn
compares a nucleotide query sequence against a nucleotide sequence
database
blastx
compares a nucleotide query sequence translated in all reading frames
against a protein sequence database
tblastn
compares a protein query sequence against a nucleotide sequence database
dynamically translated in all reading frames
tblastx
compares the six-frame translations of a nucleotide query sequence
against the six-frame translations of a nucleotide sequence database.
Please note that tblastx program cannot be used with the nr database on the BLAST Web page.