Jason Stajich | 29 Jan 20:00 2013

Re: Parsing Blast-Report extracting "Features flanking .."

We don't parse the NCBI feature info from the BLAST reports per your query. To look up a specific feature you
can use Bio::DB::GenBank to query for sequence from a specific feature by accession number - see the
HOWTOs for that.

However, most people use tools that generate SAM/BAM files with short reads - then you can use a tool like
bedtools to find overlaps of reads with the locations of features.

- download the genome and GFF for arabidopsis
- align your sRNA to the genome with a short read aligner - bowtie, bwa, others
- convert your sam to bam file with SAMtools or picard
- compare the location of features with the reads to get expression summaries or individuals reads with BEDTools

On Jan 25, 2013, at 2:20 AM, jobu <buschj <at> hhu.de> wrote:

> Am 22.01.2013 19:03, schrieb Mgavi Brathwaite:
>> What upstream and downstream elements are you interested in?
> I've got a huge pile of short RNA reads.
> Part of the question now is whether those RNA fragments originate from
> siRNA events,
> or may represent miRNAs / parts of pre-miRNAs.
> So I did an online  blast search against database nt.
> The resulting report quite often just gives subject information like this:
> -----
>> gb|CP002686.1| Arabidopsis thaliana chromosome 3, complete sequence
> Length=23459830
> -----
> Now I would like to get the hit's neighbouring regions  for further
> analysis.
> Preferably I would like to do that  in an automized way, but the only
> possible action with this kind of subject gi | description would be to
> fetch the entire chromosomal  sequence I guess ?
> However,
> right below the line above, the report states more precisely:
> ------
> Features flanking this part of subject sequence:
>   8872 bp at 5' side: cytochrome P450 90B1
>   402 bp at 3' side: U1 small nuclear ribonucleoprotein-70K
> ------
> Still I would like to have the possibility to automatically fetch the
> subject's sequence(s),
> as of now I think  parsing the report with SearchIO won't let me aquire
> that information, because SearchIO does not recognize report sections
> like those.
> I hope I did not miss any of SearchIOs capabilities, but I could not
> find any method covering my wish?!
> Right now maybe the only way to get the information I want is to
> construct my own parser and write it out into a separate file, which in
> turn again  I could read into a hash before processing the Blast-Report
> with SearchIO to combine both data for further automized work.
> I am aware though that even successfully getting the flanking features
> would leave me with the more or less wide  intergenic gap my hsp is
> located in.
> However I'm in need of a way to get the flanking features including
> their annotation and the region spanning between them.
> But I hope I do not have to get complete sequences to accomplish that,
> as this would be kind of an overkill.
> with kind regards
> Jochen
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Jason Stajich
jason.stajich <at> gmail.com
jason <at> bioperl.org