NAME

Bioperl - Getting Started

SYNOPSIS

  #!/usr/local/bin/perl

  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";
           }
        }
   }

DESCRIPTION

Bioperl is a set of Perl modules that represent useful biological objects. Some of the key objects include: Sequences, features on sequences, databases of sequences, flat file representations of sequences and similarity search results.

Because bioperl is formed from Perl modules, there are no actual useable programs in the distribution (this is not actually true. In the scripts directory there are a few useful programs. But not a great deal...). You have to write the programs which use bioperl.

It is very easy to write programs using the bioperl modules, as alot of the complex processing happens in the modules and not in the part of the program which you have to write. The idea is that you can connet up a number of the modules to do useful things. The synopsis above gives a simple script which uses bioperl. Stepping through this script, the lines mean the following things:

The first line indicates that in a UNIX manner, the /usr/local/bin/perl executable is used to execute this script. Bioperl is not a new version of perl, it just extends the standard perl for biological objects

  #!/usr/local/bin/perl

These use lines actually import the bioperl modules. Bio::Seq is the bioperl main sequence object; Bio::SeqIO is the bioperl support for sequence input/output into files

  use Bio::Seq;
  use Bio::SeqIO;

These two lines create two SeqIO streams: one for reading in sequences and one for outputting sequences. Using the

  '-argument' => value

syntax is common in bioperl. The file argument is like an argument to open() (notice that in the seqout case there is a greater-than sign, indicating opening the file for writing). You can also pass in filehandles or FileHandle objects by using the -fh argument, see SeqIO documentation for details. Many formarts in bioperl are handled, including Fasta, EMBL. GenBank, Swissprot (swiss), PIR and GCG.

  $seqin = Bio::SeqIO->new( '-format' => 'EMBL' , -file => 'myfile.dat');
  $seqout= Bio::SeqIO->new( '-format' => 'Fasta', -file => '>output.fa');

This is the main loop which will loop progressively through sequences in a file. Each call to seqio->next_seq() provides a new sequence object from the file, reading successively.

  while((my $seqobj = $seqio->next_seq())) {

This print line access fields in the sequence object directly. The seqobj->display_id is the way to access the display_id attribute of the sequence 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 gives one of these three possibilities

        if( $seqobj->moltype eq 'dna') {

The seqobj->revcom method provides the reverse complement of the seqobj object as another sequence object. The $rev variable therefore is another sequence object. For example, one could repeat the above print line for this sequence 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.

            $id  = $seqobj->display_id();
            $id  = "$id.rev";
            $rev->display_id($id);

The write_seq method on the seqout output object 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 final loop 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 GFF format, a standarised 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";
           }
        }
   }

Short Description of Objects.

Here is a very quick overview of the objects in bioperl

Bio::Seq - sequence object

   # the following methods return strings

   $seqobj->display_id(); # the human read-able id of the sequence
   $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','protein'
   $seqobj->primary_id(); # a unique id for this sequence irregardless
                          # of its display_id or accession number

   # the following methods return an array of 
   # Bio::SeqFeature objects

   $seqobj->top_SeqFeatures # The 'top level' sequence features
   $seqobj->all_SeqFeatures # All sequence features, including sub
                            # seq features

   # the following methods returns new sequence objects, but
   # do not transfer features across

   $seqobj->trunc(5,10)  # truncation from 5 to 10 as new object
   $seqobj->revcom       # reverse complements sequence
   $seqobj->translate    # translation of the sequence

Bio::SeqFeature objects:

   # attributes which 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

   # attributes which return strings
  
   $feat->primary_tag    # the main 'name' of the sequence feature,
                         # eg, 'exon'
   $feat->source_tag     # where the feature comes from, eg, 'EMBL_GenBank',
                         # or 'BLAST'

   # attributes which return sequences (these are the more restrictive
   # Bio::PrimarySeq objects, not Bio::Seq objects. The main difference
   # is that these objects do not themselves contain sequence features)

   $feat->seq            # the sequence between start,end on the
                         # correct strand of the sequence
   $feat->entire_seq     # the entire sequence, not necessarily on the 
                         # correct strand

   # useful methods for feature comparisons, for start/end points

   $feat->overlap($other)  # does feat and other overlap?
   $feat->contains($other) # is other completely within feat?
   $feat->equals($other)   # does feat and other completely agree?

   # sub features. For complex join() statements, the features
   # is one sequence feature with many sub SeqFeatures

   $feat->sub_SeqFeatures  # array of sub seq features

BLAST

...stuff on running BLAST and parsing results...

Database Access

Feel free to add to this document.