Retroviral factors promoting infectivity.

The ability of a virus particle to establish an infectious event is a fundamental property required for viral propagation and survival. Retrovirus invasion of target cells is a multistep process that begins with entry into the cytoplasm and culminates with the integration of the proviral genome into the host DNA. Along this journey, many obstacles await the retrovirus particle and undermine its infectivity. Host-cell barriers to retrovirus infection can either be basic structural components of the eukaryotic cell or specific antiretroviral activities developed by the cell to prevent the retroviral invasion. Resulting from a long host-parasite coevolution, retroviruses have developed auxiliary factors that promote infectivity by conferring the virion the ability to overcome several cellular obstacles, which interfere with the infection process. Here, we provide an overview of different retroviral auxiliary factors that promote virion infectivity, comparing their mechanism of action and highlighting common mechanistic strategies. Special attention is given to infectivity factors that remain enigmatic in the biology of retroviruses.