The nuclear import of transcription factors involves proteins termed karyopherins. Previously, we described an intracellular targeted dual nuclear localization sequence (NLS) peptide inhibitor of processes dependent upon the transcription factor NF-kappaB. We have now developed a homogeneous solution based assay and show that NF-kappaB interacts with karyopherin alpha and that the dual NLS peptide inhibits this interaction. We also show that both L- and D-amino acid containing peptides bind well to karyopherin alpha2, whereas, the L-amino acid peptides bind more efficiently than the D-amino acid peptide to karyopherin alpha1. (C) 2002 Elsevier Science (USA). All rights reserved.