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Summary

Bio::Tools::Genscan - Results of one Genscan run

Package variables

Included modules

Inherit

Bio::Tools::AnalysisResult

Synopsis

   $genscan = Bio::Tools::Genscan->new(-file => 'result.genscan');
   # filehandle:
   $genscan = Bio::Tools::Genscan->new( -fh  => \*INPUT );

   # parse the results
   # note: this class is-a Bio::Tools::AnalysisResult which implements
   # Bio::SeqAnalysisParserI, i.e., $genscan->next_feature() is the same
   while($gene = $genscan->next_prediction()) {
       # $gene is an instance of Bio::Tools::Prediction::Gene, which inherits
       # off Bio::SeqFeature::Gene::Transcript.
       #
       # $gene->exons() returns an array of 
       # Bio::Tools::Prediction::Exon objects
       # all exons:
       @exon_arr = $gene->exons();

       # initial exons only
       @init_exons = $gene->exons('Initial');
       # internal exons only
       @intrl_exons = $gene->exons('Internal');
       # terminal exons only
       @term_exons = $gene->exons('Terminal');
       # singleton exons: 
       ($single_exon) = $gene->exons();
   }

   # essential if you gave a filename at initialization (otherwise the file
   # will stay open)
   $genscan->close();

Description

The Genscan module provides a parser for Genscan gene structure prediction
output. It parses one gene prediction into a Bio::SeqFeature::Gene::Transcript-
derived object.
This module also implements the Bio::SeqAnalysisParserI interface, and thus
can be used wherever such an object fits. See Bio::SeqAnalysisParserI.

Methods

Methods description

 Title   : _add_prediction()
 Usage   : $obj->_add_prediction($gene)
 Function: internal
 Example :
 Returns :

 Title   : _has_cds()
 Usage   : $obj->_has_cds()
 Function: Whether or not the result contains the predicted CDSs, too.
 Example :
 Returns : TRUE or FALSE

 Title   : _parse_predictions()
 Usage   : $obj->_parse_predictions()
 Function: Parses the prediction section. Automatically called by
           next_prediction() if not yet done.
 Example :
 Returns :

 Title   : _prediction()
 Usage   : $gene = $obj->_prediction()
 Function: internal
 Example :
 Returns :

 Title   : _predictions_parsed
 Usage   : $obj->_predictions_parsed
 Function: internal
 Example :
 Returns : TRUE or FALSE

 Title   : _read_fasta_seq()
 Usage   : ($id,$seqstr) = $obj->_read_fasta_seq();
 Function: Simple but specialised FASTA format sequence reader. Uses
           $self->_readline() to retrieve input, and is able to strip off
           the traling description lines.
 Example :
 Returns : An array of two elements.

 Usage     : $genscan->analysis_method();
 Purpose   : Inherited method. Overridden to ensure that the name matches
             /genscan/i.
 Returns   : String
 Argument  : n/a

 Title   : next_feature
 Usage   : while($gene = $genscan->next_feature()) {
                  # do something
           }
 Function: Returns the next gene structure prediction of the Genscan result
           file. Call this method repeatedly until FALSE is returned.

           The returned object is actually a SeqFeatureI implementing object.
           This method is required for classes implementing the
           SeqAnalysisParserI interface, and is merely an alias for 
           next_prediction() at present.

 Example :
 Returns : A Bio::Tools::Prediction::Gene object.
 Args    :

 Title   : next_prediction
 Usage   : while($gene = $genscan->next_prediction()) {
                  # do something
           }
 Function: Returns the next gene structure prediction of the Genscan result
           file. Call this method repeatedly until FALSE is returned.

 Example :
 Returns : A Bio::Tools::Prediction::Gene object.
 Args    :

Methods code

sub _add_prediction {

    my ($self, $gene) = @_;

    if(! exists($self->{'_preds'})) {
	$self->{'_preds'} = [];
    }
    push(@{$self->{'_preds'}}, $gene);

}

sub _has_cds {

    my ($self, $val) = @_;

    $self->{'_has_cds'} = $val if $val;
    if(! exists($self->{'_has_cds'})) {
	$self->{'_has_cds'} = 0;
    }
    return $self->{'_has_cds'};

}

sub _initialize_state {

    my ($self,@args) = @_;

    # first call the inherited method!
    $self->SUPER::_initialize_state(@args);

    # our private state variables
    $self->{'_preds_parsed'} = 0;
    $self->{'_has_cds'} = 0;
    # array of pre-parsed predictions
    $self->{'_preds'} = [];
    # seq stack
    $self->{'_seqstack'} = [];

}

sub _parse_predictions {

    my ($self) = @_;
    my %exontags = ('Init' => 'Initial',
		    'Intr' => 'Internal',
		    'Term' => 'Terminal',
		    'Sngl' => '');
    my $gene;
    my $seqname;

    while(defined($_ = $self->_readline())) {
	if(/^\s*(\d+)\.(\d+)/) {
	    # exon or signal
	    my $prednr = $1;
	    my $signalnr = $2; # not used presently
	    if(! defined($gene)) {
		$gene = Bio::Tools::Prediction::Gene->new(
                                       '-primary' => "GenePrediction$prednr",
				       '-source' => 'Genscan');
	    }
	    # split into fields
	    chomp();
	    my @flds = split(' ', $_);
	    # create the feature object depending on the type of signal
	    my $predobj;
	    my $is_exon = grep {$_ eq $flds[1];} (keys(%exontags));
	    if($is_exon) {
		$predobj = Bio::Tools::Prediction::Exon->new();
	    } else {
		# PolyA site, or Promoter
		$predobj = Bio::SeqFeature::Generic->new();
	    }
	    # set common fields
	    $predobj->source_tag('Genscan');
	    $predobj->score($flds[$#flds]);
	    $predobj->strand((($flds[2] eq '+') ? 1 : -1));
	    my ($start, $end) = @flds[(3,4)];
	    if($predobj->strand() == 1) {
		$predobj->start($start);
		$predobj->end($end);
	    } else {
		$predobj->end($start);
		$predobj->start($end);
	    }
	    # add to gene structure (should be done only when start and end
	    # are set, in order to allow for proper expansion of the range)
	    if($is_exon) {
		# first, set fields unique to exons
		$predobj->start_signal_score($flds[8]);
		$predobj->end_signal_score($flds[9]);
		$predobj->coding_signal_score($flds[10]);
		$predobj->significance($flds[11]);
		$predobj->primary_tag($exontags{$flds[1]} . 'Exon');
		$predobj->is_coding(1);
		# Figure out the frame of this exon. This is NOT the frame
		# given by Genscan, which is the absolute frame of the base
		# starting the first predicted complete codon. By comparing
		# to the absolute frame of the first base we can compute the
		# offset of the first complete codon to the first base of the
		# exon, which determines the frame of the exon.
		my $cod_offset;
		if($predobj->strand() == 1) {
		    $cod_offset = $flds[6] - (($predobj->start()-1) % 3);
		    # Possible values are -2, -1, 0, 1, 2. -1 and -2 correspond
		    # to offsets 2 and 1, resp. Offset 3 is the same as 0.
		    $cod_offset += 3 if($cod_offset < 1);		    
		} else {
		    # On the reverse strand the Genscan frame also refers to
		    # the first base of the first complete codon, but viewed
		    # from forward, which is the third base viewed from
		    # reverse.
		    $cod_offset = $flds[6] - (($predobj->end()-3) % 3);
		    # Possible values are -2, -1, 0, 1, 2. Due to the reverse
		    # situation, {2,-1} and {1,-2} correspond to offsets
		    # 1 and 2, resp. Offset 3 is the same as 0.
		    $cod_offset -= 3 if($cod_offset >= 0);
		    $cod_offset = -$cod_offset;
		}
		# Offsets 2 and 1 correspond to frame 1 and 2 (frame of exon
		# is the frame of the first base relative to the exon, or the
		# number of bases the first codon is missing).
		$predobj->frame(3 - $cod_offset);
		# then add to gene structure object
		$gene->add_exon($predobj, $exontags{$flds[1]});		
	    } elsif($flds[1] eq 'PlyA') {
		$predobj->primary_tag("PolyAsite");
		$gene->poly_A_site($predobj);
	    } elsif($flds[1] eq 'Prom') {
		$predobj->primary_tag("Promoter");
		$gene->add_promoter($predobj);
	    }
	    next;
	}
	if(/^\s*$/ && defined($gene)) {
	    # current gene is completed
	    $gene->seq_id($seqname);
	    $self->_add_prediction($gene);
	    $gene = undef;
	    next;
	}
	if(/^(GENSCAN)\s+(\S+)/) {
	    $self->analysis_method($1);
	    $self->analysis_method_version($2);
	    next;
	}
	if(/^Sequence\s+(\S+)\s*:/) {
	    $seqname = $1;
	    next;
	}
        
	if(/^Parameter matrix:\s+(\S+)/i) {
	    $self->analysis_subject($1);
	   next;
	}
	
	if(/^Predicted coding/) {
	    $self->_has_cds(1);
	    next;
	}
	/^>/ && do {
	    # section of predicted sequences
	    $self->_pushback($_);
	    last;
	};
    }
    $self->_predictions_parsed(1);

}

sub _prediction {

    my ($self) = @_;

    return undef unless(exists($self->{'_preds'}) && @{$self->{'_preds'}});
    return shift(@{$self->{'_preds'}});

}

sub _predictions_parsed {

    my ($self, $val) = @_;

    $self->{'_preds_parsed'} = $val if $val;
    if(! exists($self->{'_preds_parsed'})) {
	$self->{'_preds_parsed'} = 0;
    }
    return $self->{'_preds_parsed'};

}

sub _read_fasta_seq {

    my ($self) = @_;
    my ($id, $seq);
    local $/ = ">";
    
    my $entry = $self->_readline();
    if($entry) {
	$entry =~ s/^>//;
	# complete the entry if the first line came from a pushback buffer
	while($entry !~ />$/) {
	    last unless $_ = $self->_readline();
	    $entry .= $_;
	}
	# delete everything onwards from an intervening empty line (at the
	# end there might be statistics stuff)
	$entry =~ s/\n\n.*$//s;
	# id and sequence
	if($entry =~ /^(\S+)\n([^>]+)/) {
	    $id = $1;
	    $seq = $2;
	} else {
	    $self->throw("Can't parse Genscan predicted sequence entry");
	}
	$seq =~ s/\s//g; # Remove whitespace
    }
    return ($id, $seq);
}

1;

}

sub analysis_method {

 #-------------
    my ($self, $method) = @_;  
    if($method && ($method !~ /genscan/i)) {
	$self->throw("method $method not supported in " . ref($self));
    }
    return $self->SUPER::analysis_method($method);

}

sub next_feature {

    my ($self,@args) = @_;
    # even though next_prediction doesn't expect any args (and this method
    # does neither), we pass on args in order to be prepared if this changes
    # ever
    return $self->next_prediction(@args);

}

sub next_prediction {

    my ($self) = @_;
    my $gene;

    # if the prediction section hasn't been parsed yet, we do this now
    $self->_parse_predictions() unless $self->_predictions_parsed();

    # get next gene structure
    $gene = $self->_prediction();

    if($gene) {
	# fill in predicted protein, and if available the predicted CDS
	#
	my ($id, $seq);
	# use the seq stack if there's a seq on it
	my $seqobj = pop(@{$self->{'_seqstack'}});
	if(! $seqobj) {
	    # otherwise read from input stream
	    ($id, $seq) = $self->_read_fasta_seq();
	    # there may be no sequence at all, or none any more
	    if($id && $seq) {
		$seqobj = Bio::PrimarySeq->new('-seq' => $seq,
					       '-display_id' => $id,
					       '-alphabet' => "protein");
	    }
	}
	if($seqobj) {
	    # check that prediction number matches the prediction number
	    # indicated in the sequence id (there may be incomplete gene
	    # predictions that contain only signals with no associated protein
	    # and CDS, like promoters, poly-A sites etc)
	    $gene->primary_tag() =~ /[^0-9]([0-9]+)$/;
	    my $prednr = $1;
	    if($seqobj->display_id() !~ /_predicted_\w+_$prednr\|/) {
		# this is not our sequence, so push back for next prediction
		push(@{$self->{'_seqstack'}}, $seqobj);
	    } else {
		$gene->predicted_protein($seqobj);
		# CDS prediction, too?
		if($self->_has_cds()) {
		    ($id, $seq) = $self->_read_fasta_seq();
		    $seqobj = Bio::PrimarySeq->new('-seq' => $seq,
						   '-display_id' => $id,
						   '-alphabet' => "dna");
		    $gene->predicted_cds($seqobj);
		}
	    }
	}
    }

    return $gene;

}

General documentation

User feedback is an integral part of the evolution of this and other
Bioperl modules. Send your comments and suggestions preferably to one
of the Bioperl mailing lists. Your participation is much appreciated.

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  bioperl-bugs@bio.perl.org
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Describe contact details here

The rest of the documentation details each of the object methods. Internal methods are usually preceded with a _