STAR: Really Kick-ass RNA-seq Aligner
Stephen Turner’s Getting Genetics Done blog posted on a new paper on ultrafast RNAseq aligning that came out in Bioinformatics. The speed of this program is amazing, BUT forget about aligning human genome in your laptop with this program. You need to have ~27GB of RAM, which is typical for servers these days. The program comes from a group at Cold Spring Harbor Lab (yes, the same place that solves the most difficult bioinformatics problems to gamble on interest rate swaps).
To align our large (exceeding 80 billon reads) ENCODE Transcriptome RNA-seq dataset we developed the Spliced Transcripts Alignment to a Reference (STAR) software based on a previously un-described RNA-seq alignment algorithm which utilizes sequential maximum mappable seed search in uncompressed suffix arrays followed by seed clustering and stitching procedure. STAR outperforms other aligners by more than a factor of 50 in mapping speed, aligning to the human genome 550 Million 2x76bp paired-end reads per hour on a modest 12-core server, while at the same time improving alignment sensitivity and precision. In addition to unbiased de novo detection of canonical junctions, STAR can discover non-canonical splices and chimeric (fusion) transcripts, and is also capable of mapping full length RNA sequences. Using Roche 454 sequencing of RT-PCR amplicons, we experimentally validated 1,960 novel intergenic splice junctions with an 80-90% success rate, corroborating the high precision of the STAR mapping strategy.
The program and code are available freely. Sadly, the paper is not.
Here are few important links -
How to run (from those impatient to read manual)
1. Each STAR run should be made from a fresh working directory. All the output files are stored in the working directory. The output files will be overwritten without a warning every time you run STAR.
2. Just like Bowtie, you need to first generate a genomic database.
STAR --runMode genomeGenerate --genomeDir /path/to/GenomeDir
--genomeFastaFiles /path/to/genome/fasta1 /path/to/genome/fasta2 --runThreadN
Please keep in mind that for STAR, you can generate the database either in regular mode or in ‘splice junction mode’ for better mapping of spliced reads.
3. Run alignment
STAR --genomeDir /path/to/GenomeDir --readFilesIn /path/to/read1
[/path/to/read2] --runThreadN \--
4. Another cool feature of STAR is that it loads the genomic database in shared memory and keeps it there for concurrent alignment runs. That saves time, if you finish one run and start another in near future.
