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Help With Counting Script

I am very new to bioperl and am trying to write a script that counts the number of sequences, number of characters, %GC content and looks for leucine zipper motifs if possible.

Here is what I have come up with thus far

#!/usr/bin/perl -w

use Bio::SeqIO;
my $seqfile = "t4.fasta" ;
my $in = Bio::SeqIO->new(-format=>'fasta',
                         -file=> $seqfile );

my $count = 0;
while ( my $seq = $in->next_seq ) {
}
print "There are $count sequences\n";

I was wondering if anyone could give me some pointers on how to get the %GC content and how to find the motif?

Thanks a million!

counts gc motif bioperl
• 5,895 views • link
updated by Andrew W • Andrew W • written by Confused • Confused

4 answers

It might not be exactly what you wanted. But here is a quick and dirty python script to get GC content, total base pairs, and number of sequences:

import sys

inFile = open(sys.argv[1],'r')

totalBP = 0
gcBP = 0
headerCount = 0
for line in inFile:
    if line[0] == ">":
        headerCount += 1
    else:
        seqLine = line.strip().lower()
        totalBP += len(seqLine)
        gcBP += seqLine.count('g')
        gcBP += seqLine.count('c')

print 'number of sequences: ' + str(headerCount)
print 'total base pairs: ' + str(totalBP)
print 'gc content: ' + str(float(gcBP) / totalBP)

Save it as YourName.py and run it by: python YourName.py mySequences.fa

• 191 views • link
written by Damian Kao Damian Kao

Sorry to drag up such an old thread, but I've just found this as I need to do the same thing! I don't have much experience with python, but a specific question here: if you passed this script a multifasta, would the totalBP counter reflect the totalBP of the WHOLE multifasta, or would it count each 'sub-fasta' when calculating the gc content of each? I realise this is somewhat academic because you could just as easily pass this each fasta in sequence in a loop to be sure but I thought I'd ask.

• 1 views • link
written by Joe Joe

the scripts runs on the entirety of the file and produces the total counts for all sequences

• 1 views • link
written by Istvan Albert Istvan Albert

my $na = $seq->seq; my $len = length $na; $totchrs += $len; # declare $totchrs outside your while loop my $gc = $na =~ tr/gcGC//; my $pergc = $gc/ $len * 100; $pergc = sprintf "%3.2f", $per_gc; # if you want it formatted

Or you can look at this script:

https://github.com/bioperl/bioperl-live/blob/master/scripts/seqstats/bp_gccalc.pl

As for finding the motif count, perhaps this is useful:

http://www.bioperl.org/wiki/FAQ#How_do_I_do_motif_searches_with_BioPerl.3F_Can_I_do_.22find_all_sequences_that_are_75.25_identical.22_to_a_given_motif.3F

• 0 views • link
updated by Istvan Albert Istvan Albert • written by Andrew W • Andrew W

Thanks a million! Is there any way to do it in perl?

• 0 views • link
updated by User 59 User 59 • written by Confused • Confused

Alternatively for counting how many sequences, you can use this:

use Bio::SeqIO;
my $fh = Bio::SeqIO->newFh(-file=>"myfile.fasta",-format=>'Fasta');
my @a= <$fh>;
print scalar @a;
• 0 views • link
written by Woa Woa

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