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  • FiReaNG3L
    Member
    • Apr 2012
    • 17

    #1

    Trim BAM file reads from 5' ends

    For a specific application I need to display the 5' ends of reads in a genome browser - so far I haven't found a way to easily trim all the reads in a BAM file down to the first basepairs. I obviously need to retain mapping information so I can't just trim the reads in FASTQ.
  • arvid
    Senior Member
    • Jul 2011
    • 156

    #2
    Define "retain mapping information"; do you need the information provided by the CIGARs? If you don't, such trimming is straightforward with a simple script chopping off the bases and qualities in the BAM (pipe "samtools view -h" into a script which skips over the headers, then for each line cuts down columns 10 and 11 to the desired length, and just replaces the CIGAR field with a *, piped into "samtools view -bS").
    If you need to retain the information in the CIGARs properly, it becomes more messy, as you'd want to think about how to handle soft-clippings and indels.
    Last edited by arvid; 05-25-2012, 03:38 AM. Reason: typo

    Comment

    • FiReaNG3L
      Member
      • Apr 2012
      • 17

      #3
      Ok, so something along the lines of what's suggested in http://seqanswers.com/forums/showpos...53&postcount=2.

      I don't think SeqMonk cares about the CIGAR information, so it should be fine.

      Comment

      • arvid
        Senior Member
        • Jul 2011
        • 156

        #4
        Yes, basically. I'd really replace the CIGAR with a * though, to make the SAM/BAM file standardized. You might want to check how to decide on which side of the read sequence in the BAM is 5'/3' (in the read, not alignment sense as I understand the SAM spec) however, didn't think about that.

        Comment

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