Fig. 6.

The tetO-CMV promoter. (A) In the tetO-CMV HIV-rtTA variant, the U3-TAR promoter region was replaced with a promoter consisting of three tetO elements coupled to the 30-bp minimal TATA box region from the CMV IE promoter and a hairpin sequence that is based on the +1/+16 sequence of the CMV transcript. This promoter was developed in another HIV-rtTA study (to be published). The EcoRV and HindIII restriction enzyme sites in the U3 and R regions, respectively, are indicated. HIV-1-derived nucleotides are shown in uppercase and non-HIV nucleotides in lowercase. Reintroduction of the three Sp1 sites from the HIV-1 LAI strain between the tetO and TATA elements resulted in the tetO-CMV-Sp1 variant. (B) Secondary structure of the new 5′-hairpin element that replaces TAR, as predicted with MFold RNA-folding software (81).