Bio::Seq - Sequence object, with features
$seqio = Bio::SeqIO->new( '-format' => 'embl' , -file => 'myfile.dat'); $seqobj = $seqio->next_seq(); # features must implement Bio::SeqFeatureI @features = $seqobj->top_SeqFeatures(); # just top level @features = $seqobj->all_SeqFeatures(); # descend into sub features $seq = $seqobj->seq(); # actual sequence as a string $seqstr = $seqobj->subseq(10,50); $ann = $seqobj->annotation(); # annotation object
A Seq object is a sequence with sequence features placed on it. The Seq object contains a PrimarySeq object for the actual sequence and also implements its interface.
In Bioperl we have 3 main players that people are going to use frequently
Bio::PrimarySeq - just the sequence and its names, nothing else. Bio::SeqFeatureI - a location on a sequence, potentially with a sequence and annotation. Bio::Seq - A sequence and a collection of sequence features (an aggregate) with its own annotation.
Although Bioperl is not tied heavily to file formats these distinctions do map to file formats sensibly and for some bioinformaticians this might help
Bio::PrimarySeq - Fasta file of a sequence Bio::SeqFeatureI - A single entry in an EMBL/GenBank/DDBJ feature table Bio::Seq - A single EMBL/GenBank/DDBJ entry
By having this split we avoid a lot of nasty circular references (sequence features can hold a reference to a sequence without the sequence holding a reference to the sequence feature).
Ian Korf really helped in the design of the Seq and SeqFeature system.
A simple and fundamental block of code
use Bio::SeqIO; my $seqIOobj = Bio::SeqIO->new(-file=>"1.fa"); # create a SeqIO object my $seqobj = $seqIOobj->next_seq; # get a Seq object
With the Seq object in hand one has access to a powerful set of Bioperl methods and Bioperl objects. This next script will take a file of sequences in EMBL format and create a file of the reverse-complemented sequences in Fasta format using Seq objects. It also prints out details about the exons it finds as sequence features in Genbank Flat File format.
use Bio::Seq; use Bio::SeqIO; $seqin = Bio::SeqIO->new( -format => 'EMBL' , -file => 'myfile.dat'); $seqout= Bio::SeqIO->new( -format => 'Fasta', -file => '>output.fa'); while((my $seqobj = $seqin->next_seq())) { print "Seen sequence ",$seqobj->display_id,", start of seq ", substr($seqobj->seq,1,10),"\n"; if( $seqobj->moltype eq 'dna') { $rev = $seqobj->revcom; $id = $seqobj->display_id(); $id = "$id.rev"; $rev->display_id($id); $seqout->write_seq($rev); } foreach $feat ( $seqobj->top_SeqFeatures() ) { if( $feat->primary_tag eq 'exon' ) { print STDOUT "Location ",$feat->start,":", $feat->end," GFF[",$feat->gff_string,"]\n"; } } }
Let's examine the script. The lines below import the Bioperl modules. Seq is the main Bioperl sequence object and SeqIO is the Bioperl support for reading sequences from files and to files
use Bio::Seq; use Bio::SeqIO;
These two lines create two SeqIO streams: one for reading in sequences and one for outputting sequences:
$seqin = Bio::SeqIO->new( -format => 'EMBL' , -file => 'myfile.dat'); $seqout= Bio::SeqIO->new( -format => 'Fasta', -file => '>output.fa');
Notice that in the "$seqout" case there is a greater-than sign, indicating the file is being opened for writing.
Using the
'-argument' => value
syntax is common in Bioperl. The file argument is like an argument to open() . You can also pass in filehandles or FileHandle objects by using the -fh argument (see Bio::SeqIO documentation for details). Many formats in Bioperl are handled, including Fasta, EMBL, GenBank, Swissprot (swiss), PIR, and GCG.
This is the main loop which will loop progressively through sequences in a file, and each call to $seqio->next_seq() provides a new Seq object from the file:
while((my $seqobj = $seqio->next_seq())) {
This print line below accesses fields in the Seq object directly. The $seqobj->display_id is the way to access the display_id attribute of the Seq object. The $seqobj->seq method gets the actual sequence out as string. Then you can do manipulation of this if you want to (there are however easy ways of doing truncation, reverse-complement and translation).
print "Seen sequence ",$seqobj->display_id,", start of seq ", substr($seqobj->seq,1,10),"\n";
Bioperl has to guess the type of the sequence, being either 'dna', 'rna', or 'protein'. The moltype attribute is one of these three possibilities.
if( $seqobj->moltype eq 'dna') {
The $seqobj->revcom method provides the reverse complement of the Seq object as another Seq object. Thus, the $rev variable is a reference to another Seq object. For example, one could repeat the above print line for this Seq object (putting $rev in place of $seqobj). In this case we are going to output the object into the file stream we built earlier on.
$rev = $seqobj->revcom;
When we output it, we want the id of the outputted object to be changed to "$id.rev", ie, with .rev on the end of the name. The following lines retrieve the id of the sequence object, add .rev to this and then set the display_id of the rev sequence object to this. Notice that to set the display_id attribute you just need call the same method, display_id(), with the new value as an argument. Getting and setting values with the same method is common in Bioperl.
$id = $seqobj->display_id(); $id = "$id.rev"; $rev->display_id($id);
The write_seq method on the SeqIO output object, $seqout, writes the $rev object to the filestream we built at the top of the script. The filestream knows that it is outputting in fasta format, and so it provides fasta output.
$seqout->write_seq($rev);
This block of code loops over sequence features in the sequence object, trying to find ones who have been tagged as 'exon'. Features have start and end attributes and can be outputted in Genbank Flat File format, GFF, a standarized format for sequence features.
foreach $feat ( $seqobj->top_SeqFeatures() ) { if( $feat->primary_tag eq 'exon' ) { print STDOUT "Location ",$feat->start,":", $feat->end," GFF[",$feat->gff_string,"]\n"; } }
The code above shows how a few Bio::Seq methods suffice to read, parse, reformat and analyze sequences from a file. A full list of methods available to Bio::Seq objects is shown below. Bear in mind that some of these methods come from PrimarySeq objects, which are simpler than Seq objects, stripped of features (see Bio::PrimarySeq for more information).
# these methods return strings, and accept strings in some cases: $seqobj->seq(); # string of sequence $seqobj->subseq(5,10); # part of the sequence as a string $seqobj->accession_number(); # when there, the accession number $seqobj->moltype(); # one of 'dna','rna',or 'protein' $seqobj->seq_version() # when there, the version $seqobj->keywords(); # when there, the Keywords line $seqobj->length() # length $seqobj->desc(); # description $seqobj->primary_id(); # a unique id for this sequence regardless # of its display_id or accession number $seqobj->display_id(); # the human readable id of the sequence
Some of these values map to fields in common formats. For example, The display_id() method returns the LOCUS name of a Genbank entry, the (\S+) following the > character in a Fasta file, the ID from a SwissProt file, and so on. The desc() method will return the DEFINITION line of a Genbank file, the description following the display_id in a Fasta file, and the DE field in a SwissProt file.
# the following methods return new Seq objects, but # do not transfer features across to the new object: $seqobj->trunc(5,10) # truncation from 5 to 10 as new object $seqobj->revcom # reverse complements sequence $seqobj->translate # translation of the sequence # if new() can be called this method returns 1, else 0 $seqobj->can_call_new # the following method determines if the given string will be accepted # by the seq() method - if the string is acceptable then validate() # returns 1, or 0 if not $seqobj->validate_seq($string) # the following method returns or accepts a Species object: $seqobj->species();
Please see Bio::Species for more information on this object.
# the following method returns or accepts an Annotation object # which in turn allows access to Annotation::Reference # and Annotation::Comment objects: $seqobj->annotation();
These annotations typically refer to entire sequences, unlike features. See Bio::AnnotationCollectionI, Bio::Annotation::Collection, Bio::Annotation::Reference, and Bio::Annotation::Comment for details.
It is also important to be able to describe defined portions of a sequence. The combination of some description and the corresponding sub-sequence is called a feature - an exon and its coordinates within a gene is an example of a feature, or a domain within a protein.
# the following methods return an array of SeqFeatureI objects: $seqobj->top_SeqFeatures # The 'top level' sequence features $seqobj->all_SeqFeatures # All sequence features, including sub-seq # features, such as features in an exon # to find out the number of features use: $seqobj->feature_count
Here are just some of the methods available to SeqFeatureI objects:
# these methods return numbers: $feat->start # start position (1 is the first base) $feat->end # end position (2 is the second base) $feat->strand # 1 means forward, -1 reverse, 0 not relevant # these methods return or accept strings: $feat->primary_tag # the name of the sequence feature, eg # 'exon', 'glycoslyation site', 'TM domain' $feat->source_tag # where the feature comes from, eg, 'EMBL_GenBank', # or 'BLAST' # this method returns the more austere PrimarySeq object, not a # Seq object - the main difference is that PrimarySeq objects do not # themselves contain sequence features $feat->seq # the sequence between start,end on the # correct strand of the sequence
See Bio::PrimarySeq for more details on PrimarySeq objects.
# useful methods for feature comparisons, for start/end points $feat->overlaps($other) # do $feat and $other overlap? $feat->contains($other) # is $other completely within $feat? $feat->equals($other) # do $feat and $other completely agree? # one can also add features $seqobj->add_SeqFeature($feat) # returns 1 if successful $seqobj->add_SeqFeature(@features) # returns 1 if successful # sub features. For complex join() statements, the feature # is one sequence feature with many sub SeqFeatures $feat->sub_SeqFeature # returns array of sub seq features
Please see Bio::SeqFeatureI and Bio::SeqFeature::Generic, for more information on sequence features.
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The rest of the documentation details each of the object methods. Internal methods are usually preceded with a "_".
Title : new Usage : $seq = Bio::Seq->new( -seq => 'ATGGGGGTGGTGGTACCCT', -id => 'human_id', -accession_number => 'AL000012', ); Function: Returns a new Seq object from basic constructors, being a string for the sequence and strings for id and accession_number Returns : a new Bio::Seq object
The PrimarySeq interface provides the basic sequence getting and setting methods for on all sequences.
These methods implement the Bio::PrimarySeq interface by delegating to the primary_seq inside the object. This means that you can use a Seq object wherever there is a PrimarySeq, and of course, you are free to use these functions anyway.
Title : seq Usage : $string = $obj->seq() Function: Returns the sequence as a string of letters. The case of the letters is left up to the implementer. Suggested cases are upper case for proteins and lower case for DNA sequence (IUPAC standard), but implementations are suggested to keep an open mind about case (some users... want mixed case!) Returns : A scalar Args : None
Title : validate_seq Usage : if(! $seq->validate_seq($seq_str) ) { print "sequence $seq_str is not valid for an object of type ", ref($seq), "\n"; } Function: Validates a given sequence string. A validating sequence string must be accepted by seq(). A string that does not validate will lead to an exception if passed to seq(). The implementation provided here does not take alphabet() into account. Allowed are all letters (A-Z) and '-','.', and '*'. Example : Returns : 1 if the supplied sequence string is valid for the object, and 0 otherwise. Args : The sequence string to be validated.
Title : length Usage : $len = $seq->length() Function: Example : Returns : Integer representing the length of the sequence. Args : None
Title : start Usage : $start = $seq->start() Function: Example : Returns : Integer representing the start of the sequence. Args : None
Title : start Usage : $start = $seq->end() Function: Example : Returns : Integer representing the end of the sequence. Args : None
Title : strand Usage : $stand = $seq->strand() Function: Example : Returns : Integer representing the strand of the sequence [0,1,-1] Args : None
Title : subseq Usage : $substring = $obj->subseq(10,40); Function: Returns the subseq from start to end, where the first base is 1 and the number is inclusive, ie 1-2 are the first two bases of the sequence Start cannot be larger than end but can be equal Returns : A string Args : 2 integers
Title : display_id Usage : $id = $obj->display_id or $obj->display_id($newid); Function: Gets or sets the display id, also known as the common name of the Seq object. The semantics of this is that it is the most likely string to be used as an identifier of the sequence, and likely to have "human" readability. The id is equivalent to the LOCUS field of the GenBank/EMBL databanks and the ID field of the Swissprot/sptrembl database. In fasta format, the >(\S+) is presumed to be the id, though some people overload the id to embed other information. Bioperl does not use any embedded information in the ID field, and people are encouraged to use other mechanisms (accession field for example, or extending the sequence object) to solve this. Notice that $seq->id() maps to this function, mainly for legacy/convenience issues. Returns : A string Args : None or a new id
Title : accession_number Usage : $unique_biological_key = $obj->accession_number; Function: Returns the unique biological id for a sequence, commonly called the accession_number. For sequences from established databases, the implementors should try to use the correct accession number. Notice that primary_id() provides the unique id for the implemetation, allowing multiple objects to have the same accession number in a particular implementation. For sequences with no accession number, this method should return "unknown". Can also be used to set the accession number. Example : $key = $seq->accession_number or $seq->accession_number($key) Returns : A string Args : None or an accession number
Title : desc Usage : $seqobj->desc($string) or $seqobj->desc() Function: Sets or gets the description of the sequence Example : Returns : The description Args : The description or none
Title : primary_id Usage : $unique_implementation_key = $obj->primary_id; Function: Returns the unique id for this object in this implementation. This allows implementations to manage their own object ids in a way the implementation can control clients can expect one id to map to one object. For sequences with no natural id, this method should return a stringified memory location. Can also be used to set the primary_id. Also notice that this method is not delegated to the internal Bio::PrimarySeq object Example : $id = $seq->primary_id or $seq->primary_id($id) Returns : A string Args : None or an id
Title : can_call_new Usage : if ( $obj->can_call_new ) { $newobj = $obj->new( %param ); } Function: can_call_new returns 1 or 0 depending on whether an implementation allows new constructor to be called. If a new constructor is allowed, then it should take the followed hashed constructor list. $myobject->new( -seq => $sequence_as_string, -display_id => $id -accession_number => $accession -alphabet => 'dna', ); Example : Returns : 1 or 0 Args : None
Title : alphabet Usage : if ( $obj->alphabet eq 'dna' ) { /Do Something/ } Function: Returns the type of sequence being one of 'dna', 'rna' or 'protein'. This is case sensitive. This is not called <type> because this would cause upgrade problems from the 0.5 and earlier Seq objects. Returns : A string either 'dna','rna','protein'. NB - the object must make a call of the type - if there is no type specified it has to guess. Args : None
These methods are inherited from the PrimarySeq interface and work as one expects, building new Bio::Seq objects or other information as expected. See Bio::PrimarySeq for more information.
Sequence Features are not transfered to the new objects. This is possibly a mistake. Anyone who feels the urge in dealing with this is welcome to give it a go.
Title : revcom Usage : $rev = $seq->revcom() Function: Produces a new Bio::Seq object which is the reversed complement of the sequence. For protein sequences this throws an exception of "Sequence is a protein. Cannot revcom" The id is the same id as the original sequence, and the accession number is also identical. If someone wants to track that this sequence has be reversed, it needs to define its own extensions To do an in-place edit of an object you can go: $seq = $seq->revcom(); This of course, causes Perl to handle the garbage collection of the old object, but it is roughly speaking as efficient as an in-place edit. Returns : A new (fresh) Bio::Seq object Args : None
Title : trunc Usage : $subseq = $myseq->trunc(10,100); Function: Provides a truncation of a sequence Example : Returns : A fresh Seq object Args : A Seq object
Title : id Usage : $id = $seq->id() Function: This is mapped on display_id Example : Returns : Args :
These methods are specific to the Bio::Seq object, and not found on the Bio::PrimarySeq object
Title : primary_seq Usage : $seq->primary_seq or $seq->primary_seq($newval) Function: Get or set a PrimarySeq object Example : Returns : PrimarySeq object Args : None or PrimarySeq object
Title : add_SeqFeature Usage : $seq->add_SeqFeature($feat); $seq->add_SeqFeature(@feat); Function: Adds the given feature object (or each of an array of feature objects to the feature array of this sequence. The object passed is required to implement the Bio::SeqFeatureI interface. Example : Returns : 1 on success Args : A Bio::SeqFeatureI implementing object, or an array of such objects.
Title : flush_SeqFeatures Usage : $seq->flush_SeqFeatures(); Function: Flushes all attached SeqFeatureI objects. To remove individual feature objects, first obtain all using all_SeqFeatures(), then flush and re-add those you want to keep. Example : Returns : 1 on success Args : None
Title : top_SeqFeatures Usage : @feat_ary = $seq->top_SeqFeatures(); Function: Returns the array of top-level features for this sequence object. Features which are not top-level are subfeatures of one or more of the returned feature objects, which means that you must traverse the subfeature arrays of each top-level feature object in order to traverse all features associated with this sequence. Use all_SeqFeatures() if you want the feature tree flattened into one single array. Example : Returns : An array of Bio::SeqFeatureI implementing objects. Args : None
Title : all_SeqFeatures Usage : @feat_ary = $seq->all_SeqFeatures(); Function: Returns the tree of feature objects attached to this sequence object flattened into one single array. Top-level features will still contain their subfeature-arrays, which means that you will encounter subfeatures twice if you traverse the subfeature tree of the returned objects. Use top_SeqFeatures() if you want the array to contain only the top-level features. Example : Returns : An array of Bio::SeqFeatureI implementing objects. Args : None
Title : feature_count Usage : $seq->feature_count() Function: Return the number of SeqFeatures attached to a sequence Example : Returns : Number of SeqFeatures Args : None
Title : species Usage : $species = $seq->species() or $seq->species($species) Function: Gets or sets the species Example : Returns : Bio::Species object Args : None or Bio::Species object
See Bio::Species for more information
Title : annotation Usage : $ann = $seq->annotation or $seq->annotation($annotation) Function: Gets or sets the annotation Example : Returns : Bio::AnnotationCollectionI object Args : None or Bio::Annotation object
See Bio::AnnotationCollectionI and Bio::Annotation::Collection for more information
To install Bio::Seq, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Bio::Seq
CPAN shell
perl -MCPAN -e shell install Bio::Seq
For more information on module installation, please visit the detailed CPAN module installation guide.