Mapping to miRBase

[Caroline Plus]

Hi guys,

How to do the mapping to miRBase to identify human miRNAs?

1. At first you should download 2 fasta files from the website: http://www.mirbase.org/ftp.shtml (and merge them into one file):
hairpin.fa Fasta format sequences of all miRNA hairpins
mature.fa Fasta format sequences of all mature miRNA sequences

3. Then, you should generate gtf for Bowtie 1 (if you want to use specifically Bowtie 1) or gff for Htseq (based on the downloaded fasta files).

I did the analysis this way, but I received very strange results (for example mir-8689, mir-7689 - I mean miRNAs with very high numbers) instead of what I was expecting (mir9, mir31, etc.- miRNAs with much smaller numbers).

Do you know maybe what I could do wrongly?

Thanks for your answer in advance!

[sbarberan]

Hi Caroline,

What I do is download the sequences from miRBase and then change all 'U' to 'T' and then create the index with bowtie-build and then align.

Could it be that because you are not changing U to T you only get hits for miRNAs with no Us?

Cheers,
sergio

[Caroline Plus]

Hello Sergio,

Thanks so much! I have just tried your approach! You are right! It is working!

Best wishes,
Caroline