carandraug

use Bio::DB::EUtilities;

my $gene_uid = 9555;
my $get_nuc = Bio::DB::EUtilities->new(
                                        -eutil  => 'elink',
                                        -db     => 'nucleotide',
                                        -dbfrom => 'gene',
                                        -id     => [$gene_uid]
                                        );
my %struct;
while (my $nuc_link = $get_nuc->next_LinkSet) {
  next unless $nuc_link->get_link_name eq 'gene_nuccore_refseqrna';
  my @nuc_uids  = $nuc_link->get_ids;
  foreach my $nuc_uid (@nuc_uids) {
    my $get_prot = Bio::DB::EUtilities->new(
                                            -eutil  => 'elink',
                                            -db     => 'protein',
                                            -dbfrom => 'nucleotide',
                                            -id     => [$nuc_uid]
                                            );
    while (my $prot_link = $get_prot->next_LinkSet) {
      next unless $prot_link->get_link_name eq 'nuccore_protein';
      my ($prot_uid) = $prot_link->get_ids;
      $struct{$nuc_uid} = $prot_uid;
    }
  }
}
foreach (keys %struct) {
  say "transcript with UID $_ encodes protein with UID $struct{$_}";
}