Model of transcription initiation from non-integrated DNA and proviral DNA. (A) viral early transcription from non-integrated DNA may initiate in the absence of Tat. Interaction between viral LTR-bound SP1 with CyclinT1 could promote the initiation of viral transcription as suggested by Yedavalli et al. . This process appears to be CDK9-independent [91,106]. (B) immediately following viral integration, Tat, generated from pre-integration transcription, can recruit HATs (Histone Acetyltransferases) to remodel nucleosomally assembled LTR, which leads to the assembly of general transcription factors. (C) Tat, can further active viral transcription through its interaction with viral RNA (Tat/TAR/CyclinT1/CDK9 complex), which leads to hyperphosphorylation of RNAP II and processive transcription.