Tumor-specific promoters are predominantly active and ensure expression of the gene under control exclusively in cancer cells. However, low activity of the promoters is an essential disadvantage for their therapy usage. To achieve a higher expression level of the therapeutic gene, herpes simplex virus thymidine kinase (HSV-tk), the Tat-TAR-system utilized by HIV-1 for increasing its own gene expression was developed. A potentiating activity of tat gene under the control of two different cancer-specific (human survivin gene and human telomerase reverse transcriptase) promoters for increasing the HSV-tk gene expression being regulated by TAR-element was evaluated, and activity of the cancer-specific promoters in the Tat-TAR-system was compared. Cotransfection of the cells with both constructions led to the tat protein synthesis and its affect the HIV-1 TAR-element. An expression level of HSV-tk gene ensured by both promoters in the binary system was close to that for strong nonspecific cytomegalovirus (CMV) promoter. Enzymatic activity of HSV-tk protein in cells containing both elements of Tat-TAR-system was two orders of magnitude higher than that in the cells transfected with HSV-tk gene under control of the cancer-specific promoter. Notably, the effect was independent of p53-status of transfected cells: HSV-tk expression level was almost the same in p53(+) and p53(-) cells. The obtained results show that the system may be used for therapy of different cancer types both p53-defective and p53-positive ones inhibiting cancer-specific promoters activity. © 2010 Pleiades Publishing, Ltd.