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  • lran2008
    Member
    • Apr 2013
    • 35

    blast result against rfam database

    Hi All,

    I am blasting my miRNA-seq fasta file against rFam data base. Here is the command line I used:
    blastn -query TOTAL_mapped_reads.fa -task megablast -db Rfam.fasta -out mapped_vs_rfam.txt -outfmt "6 qseqid sseqid qlen evalue pident nident mismatch qcovs qcovhsp"

    Then I want to retrive those reads which match tRNAs in rFam.
    There are many hits in the output (see the attached picture).

    But when I pick the first read which is shown to be 100% match with rRNA in rfam by searching it in rfam website, there is no hit.
    >62-796337
    TCCCATATGGTCTAGCGGTTAGGATTCCTGGTT

    Briefly, according to my blast result against rfam database, there is a match, but when I search the my sequence in online rfam website, there is no hit. So what is the problem?
    Attached Files
  • rhinoceros
    Senior Member
    • Apr 2013
    • 372

    #2
    Based on blastn (at ncbi) your sequence is not a tRNA. The 'best' hit is "PREDICTED: Dasypus novemcinctus WW domain-binding protein 4-like (LOC101430251), transcript variant 2, mRNA".

    Perhaps consider a more conservative evalue cutoff? Also, how did you create your Rfam db? "-db Rfam.fasta" looks rather wrong to me but maybe you just named it oddly...
    savetherhino.org

    Comment

    • lran2008
      Member
      • Apr 2013
      • 35

      #3
      Originally posted by rhinoceros View Post
      Based on blastn (at ncbi) your sequence is not a tRNA. The 'best' hit is "PREDICTED: Dasypus novemcinctus WW domain-binding protein 4-like (LOC101430251), transcript variant 2, mRNA".

      Perhaps consider a more conservative evalue cutoff? Also, how did you create your Rfam db? "-db Rfam.fasta" looks rather wrong to me but maybe you just named it oddly...
      I indeed named it oddly. Anyway, it produced results, but seems to be unreliable... The e value for 62-796337 is 1e-10 in the attached picture. So what's your suggestion for the e value cutoff?

      Comment

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