["Human U1A protein binds to hairpin II of U1 small nuclear RNA (snRNA) and, together with other proteins, forms the U1 snRNP essential in pre-mRNA splicing. U1A protein also binds to the 3' untranslated region (3'UTR) of its own pre-mRNA, inhibiting polyadenylation of the 3'end and thereby downregulating its own expression. The 3'UTR folds into an evolutionarily conserved secondary structure with two internal loops; one loop contains the sequence AUUGCAC and the other its variant AUUGUAC. The sequence AUUGCAC is also found in hairpin II of U1 snRNA; hence, U1A protein recognizes the same heptanucleotide sequence in two different structural contexts. In order to better understand the control mechanism of the polyadenylation process, we have built a model of the U1A protein-3'UTR complex based on the crystal structure of the U1A protein-hairpin II RNA complex which we determined previously.", "In the crystal structure of the U1A protein-hairpin II RNA complex the AUUGCAC sequence fits tightly into a groove on the surface of U1A protein. The conservation of the heptanucleotide in the 3'UTR strongly suggests that U1A protein forms identical sequence-specific contacts with the heptanucleotide sequence when complexed with the 3'UTR. The crystal structure of the hairpin II complex and the twofold symmetry in the 3'UTR RNA provide sufficient information to restrict the conformation of the 3'UTR RNA and have enabled us to build a model of the 3'UTR complex."] Are two structurally different RNA molecules bound by the spliceosomal protein U1A using the same recognition strategy?