We determined whether peptide nucleic acids (PNAs) are able to interact with NF-B p52 transcription factor. The binding of NF-B p52 to DNA-DNA, DNA-PNA, PNA-DNA, and PNA-PNA hybrid molecules carrying the NF-B binding sites of human immunodeficiency type 1 long terminal repeat was studied by (i) biospecific interaction analysis (BIA) using surface plasmon resonance technology, (ii) electrophoretic mobility shift, (iii) DNase I footprinting, and (iv) UV cross-linking assays. Our results demonstrate that NF-B p52 does not efficiently bind to PNA-PNA hybrids. However, a DNA-PNA hybrid molecule was found to be recognized by NF-B p52, although the molecular complexes generated exhibited low stability. From the theoretical point of view, our results suggest that binding of NF-B p52 protein to target DNA motifs is mainly due to contacts with bases; interactions with the DNA backbone are, however, important for stabilization of the protein-DNA complex. From the practical point of view, our results suggest that DNA-PNA hybrid can be recognized by NF-B p52 protein, although with an efficiency lower than DNA-DNA NF-B target molecules; therefore, our results should encourage studies on modified PNAs in order to develop potential agents for the decoy approach in gene therapy.It is well established that both constitutive and tissue-specific regulation of gene expression is operated at the transcriptional level by the interaction between nuclear proteins (transcription factors) and promoter regions containing DNA elements (transcription signals) that exhibit specific nucleotide sequences (1-4). Several reviews reporting the nucleotide sequences of transcription signals and the relative binding proteins have been published (5-7). The requirement of protein-