Distinct Pathway of Human T-Cell Leukemia Virus Type 1 Gag Punctum Biogenesis Provides New Insights into Enveloped Virus Assembly

Abstract

This report describes the results of experiments examining the pathway by which the human retroviral Gag protein is recruited to sites along the inner leaflet of the plasma membrane where Gag punctum biogenesis occurs. In particular, clever and sensitive experimental methods were devised to image in living cells fluorescently labeled Gag protein derivatives from human T-cell leukemia virus type 1 (HTLV-1) and human immunodeficiency virus type 1 (HIV-1) at the plasma membrane. The photoconvertible fluorescent protein mEos2 was strategically utilized, as the fluorescence emission of Gag at the plasma membrane could be differentiated from that of cytosolic Gag. This experimental strategy allowed for the determination of the Gag recruitment pathway into Gag puncta. For HTLV-1 Gag, puncta recruited Gag primarily from the plasma membrane, while HIV-1 Gag was recruited from the cytoplasm. These observations represent the first report of HTLV-1 particle biogenesis and its contrast to that of HIV-1. The observed differences in the Gag recruitment pathways used by HTLV-1 and HIV-1 Gag provide key information that is useful for informing the discovery of novel targets for antiretroviral therapies directed at eliminating virus infectivity and spread.