This event was inferred from the corresponding Reactome human Poll II transcription elongation event. The details specific to HIV-1 transcription elongation are described below. In the absence of the HIV-1 Tat protein, the RNA Pol II complexes associated with the HIV-1 template are non-processive. RNA Pol II is arrested after promoter clearance by the negative transcriptional elongation factors DSIF and NELF as occurs during early elongation of endogenous templates (Wada et al, 1998; Yamaguchi et al. 1999). This arrest cannot be overcome by P-TEFb mediated phosphorylation in the absence of Tat however, and elongation aborts resulting in the accumulation of short transcripts (Kao et al., 1987).