tokens: Whereas activation of the HIV-1 enhancer following T-cell stimulation is mediated largely through binding of the transcription factor NF-kappa B to two adjacent kappa B sites in the HIV-1 long terminal repeat , activation of the HIV-2 enhancer in monocytes and T cells is dependent on four cis-acting elements : a single kappa B site , two purine-rich binding sites , PuB1 and PuB2 , and a pets site .