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STAR commands

The STAR homepage:

The STAR paper:

The STAR manual:

Downloading genome FASTA and GTF files from ENSEMBL:

Generating the genome:

Note the sjdbOverhang is used for constructing the splice junction database. It should be set to (read length - 1), and according to the manual a general value of 100 will work as well.

For this limited demonstration, I am only going to align to the genes on chromosome 1, so I subset the GTF file:

grep -P '^1\t' Homo_sapiens.GRCh38.79.gtf > Homo_sapiens.GRCh38.79.chrom1.gtf

We then moved files in subdirectories, and created one for the STAR genome index:

mkdir gtf
mkdir genome
mv *.gtf gtf
mv *.fa genome
mkdir GRCh38.79.chrom1

The STAR command to generate the genome index:

STAR --runMode genomeGenerate \
--genomeDir GRCh38.79.chrom1 \
--genomeFastaFiles genome/Homo_sapiens.GRCh38.dna.chromosome.1.fa \
--sjdbGTFfile gtf/Homo_sapiens.GRCh38.79.chrom1.gtf \
--sjdbOverhang 62 

Mapping the reads:

STAR --runThreadN 12 \
--genomeDir GRCh38.79.chrom1 \
--readFilesIn fastq/SRR1039508_1.fastq fastq/SRR1039508_2.fastq