BOWTIE ALIGNMENT USING COMMAND LINES

Import data¶

We first create a working directory for our bowtie alignment and import the required input data in it:

mkdir ~/bowtie_work && cd ~/bowtie_work

wget https://ftp.flybase.net/genomes/dmel/dmel_r6.54_FB2023_05/fasta/dmel-all-chromosome-r6.54.fasta.gz \
     https://psilo.sorbonne-universite.fr/index.php/s/HYLtfo9d2eD3Q2A/download/GRH-103_R1.fastq.gz

Check the imported files using:

ll

We also need to uncompress the .gz files

gunzip *.gz

you can check the result by

ll -rt

Install required packages¶

We will need the bowtie and samtools programs:

apt update && apt install -y bowtie samtools

Clip fastq reads from their sequence adapter and output clipped sequences in a fasta format¶

cat GRH-103_R1.fastq | \
perl -ne 'if (/^([GATC]{18,})TGGAATT/){$count++; print ">$count\n"; print "$1\n"}' \
> clipped_GRH-103.fa

Check the result with

grep -c ">" clipped_GRH-103.fa

and

wc -l clipped_GRH-103.fa

Prepare dmel_r6.54 bowtie index¶

The following command line is masked. Before unmasking it, you can try to find the appropriate command line using the man command or the --help argument

Bowtie indexing command line

time bowtie-build --threads 7 dmel-all-chromosome-r6.54.fasta dmel.r6.54

Note the time here is to indicate the time consumed to index the genome, it is optional.

Align the clipped fasta reads to dmel.r6.54 using `bowtie`¶

time bowtie dmel.r6.54 -f clipped_GRH-103.fa \
                       -v 0 \
                       -k 1 \
                       -p 7 \
                       --al dmel_matched_GRH-103.fa \
                       --un unmatched_GRH-103.fa \
                       -S \
                       > GRH-103.sam

Convert SAM file to BAM file and sort the alignments by chromosome positions¶

samtools view -Sb -@ 7 GRH-103.sam | samtools sort -@ 4 -o GRH-103.bam

Check the result using

samtools view GRH-103.bam | more