Removing everything after the last underscore in the header of a fastafile

Question

[timmers]

Aloha,

I am having trouble figuring out how to remove everything after the last '_' in the sequence headers of a fasta file.

I would like this following series of headers

>ART01B_100_M7_ID100005_1
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>PAG05A_100_M7_ID102325_189
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>KIN05B_100_M7_ALT_ID230005_46
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT

to look like this:

>ART01B_100_M7_ID100005
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>PAG05A_100_M7_ID102325
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>KIN05B_100_M7_ALT_ID230005
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT

because there are various '_' in the sequence headers, this command, for example, won't work:

cat Alt_MACSE_Output.fasta | awk -F _ '/^>/ { print $1"_"$2"_"$3"_"$4 } /^[A-Z]/ {print $1}' > Alt.fasta

Can anyone help me please?

[finswimmer]

Hello and welcome to biostars timmers ,

Please use the formatting bar (especially the code option) to present your post better. I've done it for you this time.

Thank you!

Answer 1

[finswimmer]

You can do this with sed

$ sed 's/_[^_]*$//' input.fa > output.fa

fin swimmer

Answer 2

[5heikki]

awk 'BEGIN{OFS=FS="_"}{if(/^>/){NF--}}{print $0}' in.fa > out.fa

[ATpoint]

Nice and simple. Still, I think it would help OP most if you explain in a sentence or two what the command is doing in order to generalize it for upcomming problems.

[5heikki]

Sure,

BEGIN{OFS=FS="_"} Before anything is read, underscore is set as field separator (FS) and output field separator (OFS). If OFS was omitted it would default to space and we would have >ART01B 100 M7 ID100005 instead of >ART01B_100_M7_ID100005

{if(/^>/){NF--}} If a line begins with ">" (e.g. it's a header line in fasta format), number of fields (NF) is reduced by one. NF = Number of fields, $NF = the value in the last field. The value in the second last field would be referred to as $(NF-1). Thus NF-- reduces number of fields by one (it could also be NF-=1). $NF-- would reduce the value in the last field by one, e.g. 3 would become 2. I think any non-numerical would become -1 because the operation was false..

{print $0} Print the whole line, you could replace this with just "1", but IMO it's more clear to always write it like this..

Answer 3

[cpad0112]

Another sed solution:

$ sed '/>/ s/\(.*\)_.*$/\1/g' test.fa

>ART01B_100_M7_ID100005
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>PAG05A_100_M7_ID102325
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT
>KIN05B_100_M7_ALT_ID230005
TAAGAGGAGGAATTTTTCATAGAGGATTGTCTGTAGACTTAGTAATTTTTTCTCTTCATTTAGCTGGAATTTCTTCTCTT
TTAGGGGCTGTAAATTTTATTACTACAATTCTTAATTGTCGATCTTTAGGGGTTTGGTGAGATGAATTGCCCTTATTTGT

Answer 4

[Amitm]

Hi, This should work -

awk -F '_' '{if (/^>/) print $1"_"$2"_"$3"_"$4; else print $0;}' test.fasta

[Amitm]

sorry, I think this is not removing stuff from the last '_' onwards, but just printing the 1st four '_' sep values.