Several eukaryotic proteins have the ability to travel through biological membranes. Examples include the HIV-1 TAT protein, the herpes simplex virus 1 DNA-binding protein VP22, and the Drosophila Antennapedia homeotic transcription factor. The small protein transduction domains from these proteins can be fused to other macromolecules, peptides, or proteins to successfully transport them into a cell. So far, there has been no example of any prokaryotic proteins or peptides derived from prokaryotic proteins to perform a similar function. Here we show that full-length Tus protein or a peptide is capable of transporting proteins into mammalian cells from the culture media. The NLS and NES of Tus protein may be important in transducing proteins into mammalian cells. To further demonstrate the importance of the basic amino acids in the putative NLS-like sequence, we systematically mutated them and examined the subcellular distribution of green fluorescence following transfection into PC3 cells. The construct used for the mutation contains amino acids 218�C309 of Tus fused to GFP. As can be seen in Sodium Butyrate Figure 3A, alteration of any one of the basic amino acids resulted in pronounced perturbation of nuclear targeting of the fusion proteins. These GSK-J4 results suggest that each of these basic amino acids plays a crucial role in nuclear transport. Finally, we cloned amino acids KLKIKRPVK, at the end of GFP and showed that these amino acids are all that is needed for nuclear transport of GFP. For comparison with a positive control, we also cloned a SV40 NLS, a highly characterized NLS motif, similar to Tus NLS with GFP. As can be seen, GFP fluorescence is very similar in both cases, suggesting that both NLS sequences function similarly. It has been proposed that NLS sequences often overlap with the nucleic acid binding domain of proteins. It is true that the residues KLKIKRPVK of Tus protein are indeed involved in interacting with ter sequences. However, our tests show it is very unlikely that the DNA binding activity of Tus is essential for nuclear targeting.