cDNA cloning, expression and characterization of human prostaglandin F synthase

Nuclear import usually relies on the presence of nuclear localization sequences (NLSs). NLSs are recognized by NLS receptors (importins), which target their substrates to the nuclear pore. We identified the NLSs of the yeast ribosomal proteins S22 and S25 and studied the former by mutational analysis. Furthermore, in S25 the nucleolar targeting information was found to overlap with its NLS. Comparison with previously published data on yeast ribosomal protein NLSs and computer analysis indicates the existence of a novel type of ribosomal protein-specific NLS that differs from the classical Chelsky and bipartite NLSs. The existence of such a ribosomal protein-specific NLS is in accordance with the recent identification of ribosomal protein-specific importins.