Tat is required for efficient HIV-1 reverse transcription

Abstract

The ability of human immunodeficiency virus-1 (HIV-1) to undergo efficient reverse transcription is dependent on a number of parameters. These include the binding of the tRNA(3)(Lys) to the HIV-1 primer binding site and the subsequent interaction with the heterodimeric reverse transcriptase. Recently, we demonstrated that TAR RNA was also necessary for efficient HIV-1 reverse transcription. Given the fact that the Tat protein is involved in the activation of HIV-1 gene expression in conjunction with TAR, we wished to determine whether Tat might also be involved in the control of HIV-1 reverse transcription. HIV-1 virions deleted in the tat gene were unable to initiate reverse transcription efficiently upon infection of peripheral blood mononuclear cells (PBMCs). This defect was not due to decreased amounts of genomic RNA, reverse transcriptase or other HIV-1 proteins which were incorporated into the virion. Following transfection of wild-type but not mutant tat genes into cell lines producing HIV-1 lacking tat, the virions produced could be complemented for defects in reverse transcription upon subsequent infection of PBMCs. In contrast, the defect in reverse transcription seen with HIV-1 lacking the tat gene could not be complemented when the target cells rather than the producer cells contained tat. Viruses lacking tat were also defective in endogenous assays of reverse transcription, although these viruses contained similar levels of reverse transcriptase. These results indicate that the Tat protein, in addition to regulating the level of gene expression, is also important for efficient HIV-1 reverse transcription.

A Mutant Tat Protein Provides Strong Protection from HIV-1 Infection in Human CD4+T Cells

“…Although these analyses hinted that Nullbasic might be successfully delivered to target cells by lentiviral vectors, overall transduction ability of the lentiviral particles conveying Nullbasic were markedly reduced compared with controls, an outcome that could be largely attributed to a defect in reverse transcription. However, Nullbasic did not affect infectivity of MLV-A virus-like particles, indicating that Nullbasic most likely targets the HIV-1 reverse transcription complex (RTC), cellular components important for HIV-1 reverse transcription, or may act as a trans-dominant negative inhibitor given evidence that Tat can support improved HIV-1 reverse transcription (Harrich et al, 1997). The precise mechanism by which Nullbasic inhibits reverse transcription remains to be determined.…”

Ligand-induced changes in 2-aminopurine fluorescence as a probe for small molecule binding to HIV-1 TAR RNA

“…The secondary structure of TAR consists of two helical stem regions separated by three unpaired bases that form an internal bulge, and the terminal stem is capped by a 6-nt apical loop. Upon Tat binding to TAR, viral mRNA production is increased several hundredfold through a resulting increase in the elongation capacity of RNA polymerase (Harrich et al 1996(Harrich et al , 1997. Binding of Tat to TAR is mediated by a single arginine residue located in the basic portion of the protein (Calnan et al 1991a,b).…”

Tat Acetyl-acceptor Lysines Are Important for Human Immunodeficiency Virus Type-1 Replication

“…Tat is a multifunctional protein, absolutely required for virus replication and AIDS progression. Besides its primary function as the viral transcription factor, Tat has been proposed to be required for efficient reverse transcription (1). Tat is secreted from infected cells (2,3), whereupon it binds to neighboring cells through electrostatic interactions, chemokine receptors (4), or cell surface integrins (5).…”