[Bioperl-l] For a SwissProt protein to get a DNA sequence

[Sang Chul Choi]

I want to get a DNA sequence coding a swissprot protein. My swissprot ID
is Q16637. I used Bio::DB::SwissProt to get the flat file. Then, there were

several db_xref (dblinks annotation) links including

U43883 U43876 U43877 U43878 U43880 U43881 U43882 U18423 U80017 AC005031 U21914 BC000908 BC015308 BC062723 BC070242

So, I have tried to fetch and parse the first one, U43883, or I've run these codes and gotten
the following warnings and so on. The reason why I have these warnings, I think, would
be there is no U43882, and U43880 in the current fetched U43883 flat file because the last
line of code, $nuc_seq_str = $f->spliced_seq->seq;, the spliced_seq method is thought
to be parsing the CDS feature. How can I put these DNA sequences together without 
any warnings?

Thank you,

Sang Chul Choi

CDS             join(U43876.1:608..688,U43877.1:104..175,
                     U43878.1:118..237,U43879.1:84..284,U43880.1:69..221,
                     U43881.1:103..198,U43882.1:53..163,209..259)

CODE

      my $gbseq = $gb->get_Seq_by_acc($xrefid);

      # Get the CDS information
      my @features = $gbseq->all_SeqFeatures;

      # sort features by their primary tags
      for my $f (@features) {
          my $tag = $f->primary_tag;
          if ( $tag eq "CDS" ) {
              $nuc_seq_str = $f->spliced_seq->seq;


-------------------- WARNING ---------------------
MSG: cannot get remote location for U43882.1 without a valid Bio::DB::RandomAccessI database handle (like Bio::DB::GenBank)
---------------------------------------------------

-------------------- WARNING ---------------------
MSG: cannot get remote location for U43880.1 without a valid Bio::DB::RandomAccessI database handle (like Bio::DB::GenBank)
---------------------------------------------------