predictCoding-methods: Predict amino acid coding changes for variants

In Bioconductor/VariantAnnotation: Annotation of Genetic Variants

Predict amino acid coding changes for variants

Description

Predict amino acid coding changes for variants a coding regions

Usage

## S4 method for signature 'CollapsedVCF,TxDb,ANY,missing'
predictCoding(query, subject, seqSource, varAllele, ..., ignore.strand=FALSE)
## S4 method for signature 'ExpandedVCF,TxDb,ANY,missing'
predictCoding(query, subject, seqSource, varAllele, ..., ignore.strand=FALSE)
## S4 method for signature 'IntegerRanges,TxDb,ANY,DNAStringSet'
predictCoding(query, subject, seqSource, varAllele, ..., ignore.strand=FALSE)
## S4 method for signature 'GRanges,TxDb,ANY,DNAStringSet'
predictCoding(query, subject, seqSource, varAllele, ..., ignore.strand=FALSE)
## S4 method for signature 'VRanges,TxDb,ANY,missing'
predictCoding(query, subject, seqSource, varAllele, ..., ignore.strand=FALSE)

Arguments

query	A VCF, IntegerRanges, GRanges or VRanges instance containing the variants to be annotated. If query is a IntegerRanges or VRanges it is coerced to a GRanges. If a VCF is provided the GRanges returned by the rowRanges() accessor will be used. All metadata columns are ignored. When query is not a VCF object a varAllele must be provided. The varAllele must be a DNAStringSet the same length as the query. If there are multiple alternate alleles per variant the query must be expanded to one row per each alternate allele. See examples. NOTE: Variants are expected to conform to the VCF specs as described on the 1000 Genomes page (see references). Indels must include the reference allele; zero-width ranges are not valid and return no matches.
subject	A TxDb object that serves as the annotation. GFF files can be converted to TxDb objects with makeTxDbFromGFF() in the txdbmaker package.
seqSource	A BSgenome instance or an FaFile to be used for sequence extraction.
varAllele	A DNAStringSet containing the variant (alternate) alleles. The length of varAllele must equal the length of query. Missing values are represented by a zero width empty element. Ranges with missing varAllele values are ignored; those with an ‘N’ character are not translated. When the query is a VCF object the varAllele argument will be missing. This value is taken internally from the VCF with alt(<VCF>).
...	Additional arguments passed to methods. Arguments genetic.code and if.fuzzy.codon are supported for the translate function.
ignore.strand	A logical indicating if strand should be ignored when performing overlaps. When ignore.strand == TRUE the query strand is set to '*' and can overlap with any strand of the subject. The return GRanges reflects the strand of the subject hit, however, the positions and alleles reported are computed as if both were from the '+' strand. ignore.strand == FALSE requires the query and subject to have compatible strand. Again the return GRanges reports the strand of the subject hit but in this case positions and alleles are computed according to the strand of the subject.

Details

This function returns the amino acid coding for variants that fall completely ‘within’ a coding region. The reference sequences are taken from a fasta file or BSgenome. The width of the reference is determined from the start position and width of the range in the query. For guidance on how to represent an insertion, deletion or substitution see the 1000 Genomes VCF format (references).

Variant alleles are taken from the varAllele when supplied. When the query is a VCF object the varAllele will be missing. This value is taken internally from the VCF with alt(<VCF>). The variant allele is substituted into the reference sequences and transcribed. Transcription only occurs if the substitution, insertion or deletion results in a new sequence length divisible by 3.

When the query is an unstranded (*) GRanges predictCoding will attempt to find overlaps on both the positive and negative strands of the subject. When the subject hit is on the negative strand the return varAllele is reverse complemented. The strand of the returned GRanges represents the strand of the subject hit.

Value

A GRanges with a row for each variant-transcript match. The result includes only variants that fell within coding regions. The strand of the output GRanges represents the strand of the subject hit.

At a minimum, the metadata columns (accessible with mcols) include,

varAllele

Variant allele. This value is reverse complemented for an unstranded query that overlaps a subject on the negative strand.

QUERYID

Map back to the row in the original query

TXID

Internal transcript id from the annotation

CDSID

Internal coding region id from the annotation

GENEID

Internal gene id from the annotation

CDSLOC

Variant location in coding region-based coordinates. This position is relative to the start of the coding (cds) region defined in the subject annotation.

PROTEINLOC

Variant codon triplet location in coding region-based coordinates. This position is relative to the start of the coding (cds) region defined in the subject annotation.

CONSEQUENCE

Possible values are ‘synonymous’, ‘nonsynonymous’, ‘frameshift’, ‘nonsense’ and ‘not translated’. Variant sequences are translated only when the codon sequence is a multiple of 3. The value will be ‘frameshift’ when a sequence is of incompatible length. ‘not translated’ is used when varAllele is missing or there is an ‘N’ in the sequence. ‘nonsense’ is used for premature stop codons.

REFCODON

The reference codon sequence. This range is typically greater than the width of the range in the GRanges because it includes all codons involved in the sequence modification. If the reference sequence is of width 2 but the alternate allele is of width 4 then at least two codons must be included in the REFSEQ.

VARCODON

This sequence is the result of inserting, deleting or replacing the position(s) in the reference sequence alternate allele. If the result of this substitution is not a multiple of 3 it will not be translated.

REFAA

The reference amino acid column contains the translated REFSEQ. When translation is not possible this value is missing.

VARAA

The variant amino acid column contains the translated VARSEQ. When translation is not possible this value is missing.

Author(s)

Michael Lawrence and Valerie Obenchain

References

http://www.1000genomes.org/wiki/analysis/variant-call-format/ http://vcftools.sourceforge.net/specs.html

See Also

readVcf, locateVariants, refLocsToLocalLocs getTranscriptSeqs

Examples

  library(BSgenome.Hsapiens.UCSC.hg19)
  library(TxDb.Hsapiens.UCSC.hg19.knownGene)
  txdb <- TxDb.Hsapiens.UCSC.hg19.knownGene 

  ## ----------------------------
  ## VCF object as query 
  ## ----------------------------
  ## Read variants from a VCF file 
  fl <- system.file("extdata", "chr22.vcf.gz", package="VariantAnnotation")
  vcf <- readVcf(fl, "hg19")

  ## Rename seqlevels in the VCF object to match those in the TxDb.
  vcf <- renameSeqlevels(vcf, "chr22")
  ## Confirm common seqlevels
  intersect(seqlevels(vcf), seqlevels(txdb))
 
  ## When 'query' is a VCF object the varAllele argument is missing.
  coding1 <- predictCoding(vcf, txdb, Hsapiens)
  head(coding1, 3)

  ## Exon-centric or cDNA locations:
  exonsbytx <- exonsBy(txdb, "tx")

  cDNA <- mapToTranscripts(coding1, exonsbytx)
  mcols(cDNA)$TXID <- names(exonsbytx)[mcols(cDNA)$transcriptsHits]
  cDNA <- cDNA[mcols(cDNA)$TXID == mcols(coding1)$TXID[mcols(cDNA)$xHits]]

  ## Make sure cDNA is parallel to coding1
  stopifnot(identical(mcols(cDNA)$xHits, seq_along(coding1)))

  coding1$cDNA <- ranges(cDNA)

  ## ----------------------------
  ## GRanges object as query 
  ## ----------------------------
  ## A GRanges can also be used as the 'query'. The seqlevels in the VCF
  ## were adjusted in previous example so the GRanges extracted with
  ## has the correct seqlevels.
  rd <- rowRanges(vcf)
 
  ## The GRanges must be expanded to have one row per alternate allele. 
  ## Variants 1, 2 and 10 have two alternate alleles.
  altallele <- alt(vcf)
  eltROWS <- elementNROWS(altallele)
  rd_exp <- rep(rd, eltROWS)
 
  ## Call predictCoding() with the expanded GRanges and the unlisted
  ## alternate allele as the 'varAllele'.
  coding2 <- predictCoding(rd_exp, txdb, Hsapiens, unlist(altallele)) 

Bioconductor/VariantAnnotation documentation built on Nov. 2, 2024, 7:22 a.m.