Ten mutants of the simian immunodeficiency virus (SIV) SIVmac239 hearing deletions (Δ) or substitutions (subst) in the NF-κB and/or Sp1 binding elements were created, and the replicative capacities of the mutants were analyzed. All mutants, including one extensively mutagenized strain entirely missing the NF-κB and four Sp1 binding elements, replicated with wild-type kinetics and to a wild-type level in peripheral blood mononuclear cell cultures in 50 to 100% of the experiments. One group of mutants replicated very similarly to SIVmac239 in kinetics and yield in CEMx174 cells (2xNFκB≥SIVmac239≃ΔNFκB≃ΔSp1234≃subtNFκBΔsubstSp12≃substSp23), while a second group replicated with delayed or slightly delayed kinetics in CEMx174 cells (SIVmac239>substSp34>ΔNFκBΔSp1234≃ΔNFκBΔSp1>substSp1234). Reversions or additional mutations were not detected in the U3 and R regions of proviral DNA from CEMx174 cells infected with the SIVmac239 mutants. Similar results were obtained when mutants of SIVmacMER (a macrophage-competent derivative of SIVmac239) were tested in peripheral blood mononuclear cell and CEMx174 cultures. However, the growth of most mutated viruses was suppressed in primary rhesus monkey alveolar macrophages (SIVmacMER≃2xNFκB≃substNFκB>ΔNFκB>ΔNFκBΔSp1234≃ΔNFκBΔSp1>ΔSp123 4≃substSp12>substSp23≃substSp34≃substSp1234≥SIVmac239). Thus, changes in the Sp1 binding sites had the most dramatic effects on SIVmac replication in primary macrophage cultures. Analysis of long terminal repeat-driven secreted alkaline phosphatase activity in transient assays showed that, unlike human immunodeficiency virus type 1, the SIV lung terminal repeat possesses an enhancer region just upstream of the NF-κB element which maintains significant levels of basal transcription in the absence of NF-κB and Sp1 sites. This region is responsive to transactivation by Tat. In addition, the SIV TATA box was shown to be stronger than that of human immunodeficiency virus type 1. Therefore, the surprisingly high replicative capacity of NF- κB and Sp1 binding site mutants of SIVmac is due to unique features of the enhancer/promoter region.
ASJC Scopus subject areas
- Insect Science