My Brother’s Keeper
When I study retroviruses I always feel a little like I am studying something closely related to myself. Why? Well, because I kind of am. See, the human genome is not exactly virginal, and over our development a number of retroviral hangers-on have integrated but never left.
One of the characteristics of a retrovirus is that it converts its genome from RNA to DNA and then places that genome into our own. So the idea is that we replicate the viral proteins just as we replicate our own cells. However, not all viruses wind up extracting themselves, and those that don’t become what we call endogenous.
They stay with us, for good or ill, and get passed through each generation, becoming part of us. So when we look at something like HIV we also have to realize that retroviral envelope proteins were essential in mammalian placental development. And that it was the retroviral env proteins that kept us alive when our mothers immune system would have otherwise killed us in utero. A discomfiting thought.