Figure 5.

VP16–β is a DNA-tracking transcriptional activator and its DNA-loading site is an enhancer. (A) Transcription of nicked pLJ-17 and -18 and pLJ-19 and -20 (Fig. 2) by Drosophila RNA polymerase II was examined in the presence or absence of 6.25 pmol of VP16–β and 3.1 pmol of γ complex, as specified above each lane (the autoradiographic exposure for lanes 1–4 is approximately half that for lanes 5–8). (B) Transcription of nicked pLJ-17 and -19 was examined in the presence of R₃ Lac repressor (24.4 nM) in the absence (lanes 3, 5, 9, and 11) or in the presence of IPTG (20 μM) (lanes 4, 6, 10, and 12). R₃ Lac repressor (40) was a generous gift from K. S. Mathews (Rice University). Other details are specified in the legend to Fig. 4.