Fig. 6. SIN3 binding changes during the transcription cycle. (A, C, E, G and I) Images of DAPI-stained polytene chromosome spreads. (B, D, F, H and J) Images of corresponding polytene chromosome spreads stained with SIN3 antibody. Spreads are arranged according to developmental timing, from PS1 (A and B) to PS9 (I and J). In each panel, the red arrow indicates the puff at 74EF, the yellow arrow the puff at 75B and the white arrow the puff at 78D. The degree of puffing at 78D relative to that at 74EF and 75B was one of several criteria used to determine the puff stage, as designated by Ashburner (1972). Panels are shown at the same magnification.