transcripts {GenomicFeatures} | R Documentation

## Extract genomic features from a TxDb-like object

### Description

Generic functions to extract genomic features from a TxDb-like object. This page documents the methods for TxDb objects only.

### Usage

    transcripts(x, ...)
    ## S4 method for signature 'TxDb'
    transcripts(x, columns=c("tx_id", "tx_name"), filter=NULL, use.names=FALSE)

    exons(x, ...)
    ## S4 method for signature 'TxDb'
    exons(x, columns="exon_id", filter=NULL, use.names=FALSE)

    cds(x, ...)
    ## S4 method for signature 'TxDb'
    cds(x, columns="cds_id", filter=NULL, use.names=FALSE)

    genes(x, ...)
    ## S4 method for signature 'TxDb'
    genes(x, columns="gene_id", filter=NULL, single.strand.genes.only=TRUE)

    ## S4 method for signature 'TxDb'
    promoters(x, upstream=2000, downstream=200, use.names=TRUE, ...)

### Arguments

`x` | A TxDb object.
`...` | For the `transcripts`, `exons`, `cds`, and `genes` generic functions: arguments to be passed to methods. For the `promoters` method for TxDb objects: arguments to be passed to the internal call to `transcripts`.
`columns` | Columns to include in the output. Must be `NULL` or a character vector as given by the `columns` method. With the following restrictions: `"TXCHROM"` and `"TXSTRAND"` are not allowed for `transcripts`. `"EXONCHROM"` and `"EXONSTRAND"` are not allowed for `exons`. `"CDSCHROM"` and `"CDSSTRAND"` are not allowed for `cds`. If the vector is named, those names are used for the corresponding column in the element metadata of the returned object.
`filter` | Either `NULL` or a named list of vectors to be used to restrict the output. Valid names for this list are: `"gene_id"`, `"tx_id"`, `"tx_name"`, `"tx_chrom"`, `"tx_strand"`, `"exon_id"`, `"exon_name"`, `"exon_chrom"`, `"exon_strand"`, `"cds_id"`, `"cds_name"`, `"cds_chrom"`, `"cds_strand"` and `"exon_rank"`.
`use.names` | `TRUE` or `FALSE`. If `TRUE`, the feature names are set as the names of the returned object, with NAs being replaced with empty strings.
`single.strand.genes.only` | `TRUE` or `FALSE`. If `TRUE` (the default), then genes are returned in a GRanges object and those genes that cannot be represented by a single genomic range (because they have exons located on both strands of the same reference sequence or on more than one reference sequence) are dropped with a message. If `FALSE`, then all the genes are returned in a GRangesList object with the columns specified thru the `columns` argument set as top level metadata columns. (Please keep in mind that the top level metadata columns of a GRangesList object are not displayed by the `show()` method.)
`upstream` | For `promoters` : An `integer(1)` value indicating the number of bases upstream from the transcription start site. For additional details see `?`promoters,GRanges-method``.
`downstream` | For `promoters` : An `integer(1)` value indicating the number of bases downstream from the transcription start site. For additional details see `?`promoters,GRanges-method``.

### Details

These are the main functions for extracting transcript information from a TxDb-like object. These methods can restrict the output based on categorical information. To restrict the output based on interval information, use the `transcriptsByOverlaps`, `exonsByOverlaps`, and `cdsByOverlaps` functions.

The `promoters` function computes user-defined promoter regions for the transcripts in a TxDb-like object. The return object is a `GRanges` of promoter regions around the transcription start site the span of which is defined by `upstream` and `downstream`. For additional details on how the promoter range is computed and the handling of `+` and `-` strands see `?`promoters,GRanges-method``.

### Value

A GRanges object. The only exception being when `genes` is used with `single.strand.genes.only=FALSE`, in which case a GRangesList object is returned.

### Author(s)

M. Carlson, P. Aboyoun and H. Pagès

### See Also

- `transcriptsBy` and `transcriptsByOverlaps` for more ways to extract genomic features from a TxDb-like object.

- `transcriptLengths` for extracting the transcript lengths (and other metrics) from a TxDb object.

- `exonicParts` and `intronicParts` for extracting non-overlapping exonic or intronic parts from a TxDb-like object.

- `extractTranscriptSeqs` for extracting transcript (or CDS) sequences from reference sequences.

- `coverageByTranscript` for computing coverage by transcript (or CDS) of a set of ranges.

- select-methods for how to use the simple "select" interface to extract information from a TxDb object.

- `microRNAs` and `tRNAs` for extracting microRNA or tRNA genomic ranges from a TxDb object.

- `id2name` for mapping TxDb internal ids to external names for a given feature type.

- The TxDb class.

### Examples

    txdb_file <- system.file("extdata", "hg19_knownGene_sample.sqlite",
                             package="GenomicFeatures")
    txdb <- loadDb(txdb_file)

    ## ---------------------------------------------------------------------
    ## transcripts()
    ## ---------------------------------------------------------------------

    tx1 <- transcripts(txdb)
    tx1

    transcripts(txdb, use.names=TRUE)
    transcripts(txdb, columns=NULL, use.names=TRUE)

    filter <- list(tx_chrom = c("chr3", "chr5"), tx_strand = "+")
    tx2 <- transcripts(txdb, filter=filter)
    tx2

    ## Sanity checks:
    stopifnot(
      identical(mcols(tx1)$tx_id, seq_along(tx1)),
      identical(tx2, tx1[seqnames(tx1) == "chr3" & strand(tx1) == "+"])
    )

    ## ---------------------------------------------------------------------
    ## exons()
    ## ---------------------------------------------------------------------

    exons(txdb, columns=c("EXONID", "TXNAME"),
                filter=list(exon_id=1))
    exons(txdb, columns=c("EXONID", "TXNAME"),
                filter=list(tx_name="uc009vip.1"))

    ## ---------------------------------------------------------------------
    ## genes()
    ## ---------------------------------------------------------------------

    genes(txdb)  # a GRanges object
    cols <- c("tx_id", "tx_chrom", "tx_strand",
              "exon_id", "exon_chrom", "exon_strand")
    ## By default, genes are returned in a GRanges object and those that
    ## cannot be represented by a single genomic range (because they have
    ## exons located on both strands of the same reference sequence or on
    ## more than one reference sequence) are dropped with a message:
    single_strand_genes <- genes(txdb, columns=cols)

    ## Because we've returned single strand genes only, the "tx_chrom"
    ## and "exon_chrom" metadata columns are guaranteed to match
    ## 'seqnames(single_strand_genes)':
    stopifnot(identical(as.character(seqnames(single_strand_genes)),
                        as.character(mcols(single_strand_genes)$tx_chrom)))
    stopifnot(identical(as.character(seqnames(single_strand_genes)),
                        as.character(mcols(single_strand_genes)$exon_chrom)))

    ## and also the "tx_strand" and "exon_strand" metadata columns are
    ## guaranteed to match 'strand(single_strand_genes)':
    stopifnot(identical(as.character(strand(single_strand_genes)),
                        as.character(mcols(single_strand_genes)$tx_strand)))
    stopifnot(identical(as.character(strand(single_strand_genes)),
                        as.character(mcols(single_strand_genes)$exon_strand)))

    all_genes <- genes(txdb, columns=cols, single.strand.genes.only=FALSE)
    all_genes  # a GRangesList object
    multiple_strand_genes <- all_genes[elementNROWS(all_genes) >= 2]
    multiple_strand_genes
    mcols(multiple_strand_genes)

    ## ---------------------------------------------------------------------
    ## promoters()
    ## ---------------------------------------------------------------------

    ## This:
    promoters(txdb, upstream=100, downstream=50)
    ## is equivalent to:
    promoters(transcripts(txdb, use.names=TRUE), upstream=100, downstream=50)

    ## Extra arguments are passed to transcripts(). So this:
    columns <- c("tx_name", "gene_id")
    promoters(txdb, upstream=100, downstream=50, columns=columns)
    ## is equivalent to:
    promoters(transcripts(txdb, columns=columns, use.names=TRUE),
              upstream=100, downstream=50)

[Package GenomicFeatures version 1.40.1 Index]