Hi all,

I am analyzing miRNA sequencing now. My data is 51bp, single -ended and ~5 M reads. I want to remove the adapter sequences from the reads before mapping to the genomes/known miRNA database.

My 3' adapter sequence is : 5-AGATCGGAAGAGCACACGTCT-3. I found that many reads only contain part of the 3' adapter sequence. I am using FASTX-toolkit to clip it off. How many bases should I put in the " Enter custom clipping sequence" ? Because in the output files, I end up with more reads when putting the whole 3 adapter sequence than putting only first 8 nt.

Also, miRNA is about 17-25 nt long, I guess that the rest of the reads (51-21=30bp) must contain part or whole 5's adapter sequence or the by-product of mRNA/tRNA degradation. So I think that I have to trim the 5' adapter as well.

Any suggestion will be highly appreciated

Thanh