my %ibase;
$ibase{"A"} = "T";
$ibase{"T"} = "A";
$ibase{"C"} = "G";
$ibase{"G"} = "C";
$ibase{"N"} = "N";
sub seq_inverse
{
	my ($nseq) = @_;
	my @seq = split(m//,$nseq);
	my $lim = @seq;
	my $inv = "";

	$inv .= $ibase{$seq[$lim]} while($lim > 0 and $lim--);

	return $inv;
}