Fig. 4

Self-inactivating (SIN) lentiviral vectors. A Non-SIN lentiviral vectors contain two wild-type HIV-1 LTRs, each comprised of a U3, R and U5 region. The U3 region contains promoter/enhancer regions from which transcription initiates at the junction between U3 and R in the 5′ LTR and terminates at the junction between R and U5 in the 3′ LTR. Viral transcripts thus lack the 5′ U3 and the 3′ U5, which are regained by duplication from each end upon reverse transcription. B In SIN lentiviral vectors, the 5′ U3 region is replaced by a heterologous promotor, such as CMV, whereas part of the 3′ U3 region has been deleted. When the 3′ U3 region of SIN vectors are duplicated, the deletion in the 3′ U3 (ΔU3) is transferred to the 5′ LTR, rendering the integrated lentiviral vector remote of viral promoter/enhancer regions