Bioconductor Rtracklayer

rtracklayer

Dependencies & Environment

Package-intrinsic requirements from the Bioconductor landing page — reproduce in any R environment.

• Version: 1.72.0 · Bioconductor: 3.23 · R: ≥ 4.6
• Depends: GenomicRanges
• Imports: XML, BiocGenerics, S4Vectors, IRanges, XVector, Seqinfo, Biostrings, curl, httr, Rsamtools, GenomicAlignments, BiocIO, restfulr
• System requirements: URL
• Install: BiocManager::install("rtracklayer")

When to Use

• Genomic Track Import/Export: Importing and exporting genomic annotation tracks (e.g., BED, GFF, WIG) into R as GRanges objects using import and export.
• UCSC Genome Browser Interaction: Interacting programmatically with the UCSC genome browser via browserSession.
• Custom Track Uploads: Uploading custom annotation tracks to a genome browser using the track<- function.
• UCSC Table Queries: Querying and downloading built-in UCSC tracks (like RepeatMasker) using ucscTableQuery and getTable.

When NOT to Use

• For core manipulation of genomic intervals without file I/O, use GenomicRanges instead.
• For parsing raw sequencing alignments, use GenomicAlignments or Rsamtools instead, as rtracklayer is designed for annotation tracks.

Data Requirements

• Input Formats: BED, GFF (v1/2/3), WIG, and other browser-supported formats.
• R Representation: Genomic coordinates must be 1-based when represented as GRanges in R.
• Genome Build: Valid genome build identifiers (e.g., "hg18", "hg19") for UCSC integration.

Key Parameters

• format: Explicitly specifies the file format (e.g., "bed", "gff1") for import or export.
• name: Character vector identifying the track within a browserSession.
• range: A GRanges object specifying the genomic segment to view or download.
• pack: Instructs the browser to use the "pack" mode for viewing a track.
• track: Specifies the name of the track to query in ucscTableQuery.
• table: Specifies the specific table within a track to retrieve via ucscTableQuery.

Best Practices

• Use GRangesForUCSCGenome to formally associate interval data with a UCSC genome build and validate bounds before uploading.
• Subset large GRanges tracks before uploading or viewing (e.g., targetTrack[1:10]) to avoid overwhelming the browser session.
• Rely on the default "auto" format detection in export and import which derives the format from the file extension.

Common Pitfalls

• Coordinate System Confusion: R and GRanges use 1-based coordinates, while formats like BED use 0-based. Fix: rtracklayer handles this automatically during import/export, so avoid manual coordinate shifting.
• Opening too many browser tabs: Changing the view state in UCSC opens a new page in the web browser. Fix: Consolidate view adjustments or use browseGenome to load tracks and set the view in a single call.

Alternatives

• GenomicRanges: For in-memory manipulation of genomic intervals without external browser interaction.
• BSgenome: For retrieving and manipulating full genome sequences rather than annotation tracks.

Citations

• Lawrence M, et al. (2009) "Software for Computing and Annotating Genomic Ranges." PLoS Computational Biology.
• Lawrence M, et al. (2007) "rtracklayer: an R package for interfacing with genome browsers." Bioinformatics.

References

• Homepage: https://bioconductor.org/packages/rtracklayer
• Vignette: https://bioconductor.org/packages/release/bioc/vignettes/rtracklayer/inst/doc/rtracklayer.pdf

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