This example of using a sequence called 'structure' to force the first four nucleotides to be unpaired ('s') and the next 3 to pair with something ('d'). The middle part is forced to form specific base-pairs as indicated by parentheses.

   >structure
   ssssddd.................(((.......)))...............................
   >gca_bovine
   AGCCCUGUGGUGAAUUUACACGUUGAAUUGCAAAUUCAGAGAAGCAGCUUCAAU-UCUGCCGGGGCUU
   >gca_chicken
   GACUCUGUAGUGAAGU-UCAUAAUGAGUUGCAAACUCGUUGAUGUACACUAA-AGUGUGCCGGGGUCU
   >gca_mouse
   GGUCUUAAGGUGAUA-UUCAUGUCGAAUUGCAAAUUCGAAGGUGUAGAGAAAU-CUCUACUAAGACUU
   >gca_rat
   AGCCUUAAGGUGAUU-AUCAUGUCGAAUUGCAAAUUCGAAGGUGUAGAGAAUCU-UCUACUAAGGCUU