Transactivator of transcription (TAT) protein is produced by HIV-1 and is involved in the induction of HIV-associated neurologic disorders (HAND). TAT is a neurotoxin that infects neurons, which HIV is unable to do. In neurons, TAT increases the number of inhibitory synapses and decreases the number of excitatory synapses in a Ca2+-dependent manner. TAT also activates microglia and other myeloid cells, disrupting cytokine/chemokine homeostasis and inducing neuroinflammation. This peptide sequence (YGRKKRRQRRRGYGRKKRRQRRRG) represents two back-to-back protein transduction (cell-penetrating) domains of TAT.