BACKGROUND: Nucleobase-bearing peptides and their interaction with DNA and RNA are an important topic in the development of therapeutic approaches. On one hand, they are highly effective for modulating the nucleic-acid-based biological processes. On the other hand, they permit to overcome some of the main factors limiting the therapeutic efficacy of natural oligonucleotides, such as their rapid degradation by nucleases. METHODS AND RESULTS: This article describes the synthesis and characterization of a novel thymine-bearing nucleoamino acid based on the l-diaminopropionic acid (l-Dap) and its solid phase oligomerization to α-peptides (oligoDapT), characterized using mass spectrometry, spectroscopic techniques, and scanning electron microscopy (SEM) analysis. The interaction of the obtained nucleopeptide with DNA and RNA model systems as both single strands (dA(12), rA(12), and poly(rA)) and duplex structures (dA(12)/dT(12) and poly(rA)/poly(rU)) was investigated by means of circular dichroism (CD) and ultraviolet (UV) experiments. From the analysis of our data, a clear ability of the nucleopeptide to bind nucleic acids emerged, with oligoDapT being able to form stable complexes with both unpaired and double-stranded DNA and RNA. In particular, dramatic changes in the dA(12)/dT(12) and poly(rA)/poly(rU) structures were observed as a consequence of the nucleopeptide binding. CD titrations revealed that multiple peptide units bound all the examined nucleic acid targets, with T(Ldap)/A or T(Ldap)/A:T(U) ratios >4 in case of oligoDapT/DNA and ~2 in oligoDapT/RNA complexes. CONCLUSION: Our findings seem to indicate that Dap-based nucleopeptides are interesting nucleic acid binding-tools to be further explored with the aim to efficiently modulate DNA- and RNA-based biological processes.