Binding of HIV-1 Tat to heparan sulfate proteoglycans is competed out by the heparin-binding factor bFGF; Cell membrane heparin sulfate proteoglycans bind to the basic region of HIV-1 Tat (amino acids 49–57) and act as receptors for extracellular Tat uptake, an effect that may contribute to the angiogenic properties of Tat in promoting Kaposi's sarcoma. Here, TAT is linked to Kaposi's sarcoma.