Question: STAR mapped more reads to transcriptome
0
gravatar for tianleivv
2.5 years ago by
tianleivv30
tianleivv30 wrote:

Hi,

I am following ENCODE pipeline to analyze my RNA-Seq data. However, STAR gives me more reads in the Aligned.toTranscriptome.out.bam compared to the Aligned.sortedByCoordinate.bam, which means it aligned more reads to transcriptome rather than genome. This is beyond my understanding. Did anyone meet this problem? Thanks a lot!

Best, Lei

rna-seq • 2.3k views
ADD COMMENTlink written 2.5 years ago by tianleivv30
1

It's hard to say w/o knowing specifically how you ran STAR. Maybe a difference in the total # of alignments (which may filter more reads in the genome alignment vs transcriptome)?

ADD REPLYlink written 2.5 years ago by Chris Fields2.1k

Hi Chris, Thanks for your reply! I am actually following the ENCODE STAR+RSEM pipeline (https://github.com/ENCODE-DCC/long-rna-seq-pipeline/blob/master/DAC/STAR_RSEM.sh). I think no matter how I ran STAR, it should filter the reads equally for these mapped to transcriptome and genome. Thus, reads mapped to genome should always no less than reads mapped to transcriptome. Lei

ADD REPLYlink modified 2.5 years ago by h.mon28k • written 2.5 years ago by tianleivv30
1

It is still hard to say, because we don't know what are the numbers you are talking about. Is it about total counts to genes / transcripts provided by the two methods? Or is it information about number of mapped reads from STAR logs? Or did you run something like samtools flagstat?

Besides, you showed the script you run, but not how you run the script. What flags did you pass to the script?

ADD REPLYlink written 2.5 years ago by h.mon28k
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