Pep-1 peptide is a well-known cell penetrating peptide (PTD, protein transduction domain) that transports full-length proteins to the nucleus of the cell. Pep-1 is a short amphipathic peptide consisted of a hydrophobic tryptophan-rich domain and a hydrophilic lysine-rich domain separated by a spacer. Pep-1 localizes rapidly (<10 min) to the nucleus of the cell via an endocytosis-independent internalization process. The Pep-1 peptide is able to efficiently deliver a variety of peptides and proteins in living cells in a fully biological active form.H-Lys-Glu-Thr-Trp-Trp-Glu-Thr-Trp-Trp-Thr-Glu-Trp-Ser-Gln-Pro-Lys-Lys-Lys-Arg-Lys-Val-OH or H-KETWWETWWTEWSQPKKKRKV-OH