Morphologic changes in human immunodeficiency virus type 1 virions secondary to intravirion reverse transcription: evidence indicating that reverse transcription may not take place within the intact viral core.

In the past, retroviral endogenous reverse transcription (ERT) was considered an artificial process, secondary to permeabilization of the viral envelope by detergents or amphipathic peptides. However, recently we have demonstrated that ERT may occur in a variety of lentiviruses without detergent treatment and may lead to increased infectivity of lentivirions in initially quiescent T lymphocytes and nonproliferating cells, such as macrophages. As full-length reverse transcripts could be synthesized within lentiviral particles, it is worth evaluating the potential alterations in lentiviral morphology due to the stimulation of intravirion reverse transcription. Using quantitative DNA-polymerase chain reaction (PCR) and transmission electron microscopy (TEM), we characterized critical alterations in human immunodeficiency virus type 1 (HIV-1) virions after stimulation of intravirion reverse transcription. Intravirion reverse transcription in HIV-1 virions was stimulated using deoxyribonucleoside triphosphates (dNTPs) and physiologic polyamines. Our studies indicated that HIV-1 virions, in which intravirion reverse transcription was stimulated, showed dissolution of the p24-shelled viral core and absence of the core-envelope linkage (CEL) region by TEM. These changes in the structure of the core correlate with the in vitro alterations in virion infectivity on primary cells. Stimulation of intravirion HIV-1 reverse transcription leads to morphologic changes in the viral particles that suggest changes in the compact viral core, which is consistent with active reverse transcription before infection of target cells. Further, via this unique approach, we suggest that intravirion or intracellular reverse transcription of HIV-1 is unlikely to take place within intact viral cores made up of p24-containing outer shells. As such, these results suggest a new approach to further dissect the intravirion or intracellular reverse transcription machinery of lentiviruses.