Aim. Protein fragments coding for nuclear (NLS) and/or nucleolar (NoLS) localization signals are often used for the investigation of the mechanisms of protein accumulation inside the nuclei and the nucleoli, but it is possible that accumulation mechanisms in full-length proteins will be different. Methods. Here, we compared the nuclear and nucleolar accumulation of HIV-1 Tat protein and its basic domain containing both NLS and NoLS. Results. The pattern of accumulation of the basic domain of HIV-1 Tat protein in the nuclei and the nucleoli is different from that of full-length Tat proteins: the basic domain is accumulated weaker inside the nuclei, but stronger in the nucleoli as compared to the full-length protein. Conclusion. The molecular mechanism of nuclear and nucleolar accumulation of full-length Tat protein might be different from that of the Tat protein fragments.