Functional differences between the long terminal repeat transcriptional promoters of human immunodeficiency virus type 1 subtypes A through G

The current human immunodeficiency virus type 1 (HIV-1) shows an increasing number of distinct viral subtypes, as well as viruses that are recombinant s of at least two subtypes, Although no biological differences have been de scribed so far for viruses that belong to different subtypes, there is cons iderable sequence variation between the different HIV-1 subtypes, The HIV-1 long terminal repeat (LTR) encodes the transcriptional promoter, and the L TR of subtypes A through G was cloned and analyzed to test if there are sub type-specific differences in gene expression. Sequence analysis demonstrate d a unique LTR enhancer-promoter configuration for each subtype. Transcript ion assays with luciferase reporter constructs showed that all subtype LTRs are functional promoters with a low basal transcriptional activity and a h igh activity in the presence of the viral Tat transcriptional activator pro tein. All subtype LTRs responded equally well to the Tat trans activator pr otein of subtype B, This result suggests that there are no major difference s in the mechanism of Tat-mediated trans activation among the subtypes. Nev ertheless, subtype-specific differences in the activity of the basal LTR pr omoter were measured in different cell types. Furthermore, we measured a di fferential response to tumor necrosis factor alpha treatment, and the induc tion level correlated with the number of NF-kappa B sites in the respective LTRs, which varies from one (subtype E) to three (subtype C), In general, subtype E was found to encode the most potent LTR, and we therefore inserte d the core promoter elements of subtype E in the infectious molecular clone of the LAI isolate (subtype B), This recombinant LAI-E virus exhibited a p rofound replication advantage compared with the original LAI virus in the S upT1 T-cell line, indicating that subtle differences in LTR promoter activi ty can have a significant impact on viral replication kinetics. These resul ts suggest that there may be considerable biological differences among the HIV-1 subtypes.