rtracklayer currently considers GFF3 files to be right-open. The GFF3 spec
states that start is always <= end, and that zero-width intervals have start
== end. To me, this suggests that they are right-open. Otherwise, you need
some other way to distinguish zero vs. one width intervals, which is crazy.

I can see the point though that for most use-cases zero and non-zero width
intervals are not mixed, and the user usually knows which is which. But
that's pretty poor design.

Originally, rtracklayer used closed intervals for GFF3, but I changed that a
couple of years ago after seeing the genomeIntervals documentation and
re-reading the spec.

Perhaps we can assume that since previous versions of GFF are clearly
specified to have closed intervals, that GFF3 follows the same convention,
by default.

I'll make that change. Users will need to modify the imported data structure
if they want to consider zero-width intervals.

I've personally never used GFF, so this is all pretty vague to me.

Michael

On Thu, Apr 14, 2011 at 5:16 AM, Kathi Zarnack <zarnack@ebi.ac.uk> wrote:

> Hi,
>
> I am using the package rtracklayer to import transcript.gtf files produced
> by Cufflinks.
>
> As I understand the gff3 specification, feature coordinates are given as
> "start and end of the feature, in 1-based integer coordinates" (also
> discussed in this mailing list lately), meaning that the line below from my
> gtf file corresponds to an exons ranging from 1310534 to 1310771.
>
> original line from the gtf file:
> chr1    transcripts_C4    exon    1310534    1310771    78    -    .
>  Parent=CUFF.1065.1
>
> However, upon rtracklayer import, the exon ends at 1310770 (see below).
> Thus, as I understand it, rtracklayer import.gff() interprets gtf as
> "1-based right-open" (upon export using export.gff3(), it also becomes
> 1310771 again). I tried importing with explicitly specifying version="3" and
> also updated to the latest rtracklayer version, but neither helped. Is this
> a bug in the rtracklayer function or am I interpreting the gff coordinates
> wrongly? Any comments will be appreciated.
>
> Thanks for your help.
>
> Best regards,
> Kathi
>
>
> > library(rtracklayer)
> Loading required package: RCurl
> Loading required package: bitops
>
> >
> gff=import.gff("/nfs/research2/luscombe/kathi/data/expression_data/hnRNPC_mRNAseq/cufflinks_0.9.3/cufflinks_C4/transcripts_C4.gtf",
> + genome="hg19",asRangedData=FALSE)
>
> > gff[177]
> GRanges with 1 range and 11 elementMetadata values
>   seqnames             ranges strand |        type       source       phase
>      <Rle>          <IRanges>  <Rle> | <character>  <character> <character>
> [1]     chr1 [1310534, 1310770]      - |        exon Cufflinks_C4
>  NA
>     conf_hi   conf_lo       cov      FPKM      frac          ID      Parent
>   <numeric> <numeric> <numeric> <numeric> <numeric> <character> <character>
> [1]        NA        NA        NA        NA        NA          NA
> CUFF.1065.1
>       score
>   <numeric>
> [1]        78
>
> seqlengths
>  chr1 chr10 chr11 chr12 chr13 chr14 ...  chr7  chr8  chr9  chrM  chrX  chrY
>   NA    NA    NA    NA    NA    NA ...    NA    NA    NA    NA    NA    NA
>
> > export.gff3(gff[177],"test_export.gtf")
>
>
> [zarnack@ebi-001 ~]$ more test_export.gtf
> ##gff-version 3
> ##date 2011-04-14
> chr1    Cufflinks_C4    exon    1310534    1310771    78    -    NA
>  Parent=CUFF.1065.1
>
>
> > sessionInfo()
> R version 2.12.0 (2010-10-15)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
> [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C             [3]
> LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8   [5] LC_MONETARY=C
>        LC_MESSAGES=en_GB.UTF-8  [7] LC_PAPER=en_GB.UTF-8       LC_NAME=C
>            [9] LC_ADDRESS=C               LC_TELEPHONE=C           [11]
> LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> other attached packages:
> [1] rtracklayer_1.10.6 RCurl_1.5-0        bitops_1.0-4.1
> loaded via a namespace (and not attached):
> [1] Biobase_2.10.0      Biostrings_2.18.0   BSgenome_1.18.1   [4]
> GenomicRanges_1.2.1 IRanges_1.8.9       tools_2.12.0      [7] XML_3.2-0
>
>
> --
> Dr. Kathi Zarnack
> Luscombe Group
> European Bioinformatics Institute
> Wellcome Trust Genome Campus
> Hinxton, Cambridge
> CB10 1SD, UK
> tel +44 1223 494 526
>
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