The intact retroviral Env glycoprotein of human foamy virus is a trimer

Electron microscopy of negatively stained human foamy virus particles provi des direct evidence for the trimeric nature of intact Env surface glycoprot eins. Three-dimensional image reconstruction reveals that the Env trimer is a tapering spike 14 nm in length. The spikes were often arranged in hexago nal rings which shared adjacent Env trimers.