Fig. 6. Promoter dependency of the H1 effect on transcription. (A) In vitro transcription analysis of wild-type MMTV and HRE/MMTVΔ minichromosomes reconstituted in the presence or absence of histone H1. Chromatin reconstituted with or without histone H1 was incubated with purified recombinant PR and NF1 as indicated and transcribed in vitro with HeLa nuclear extract (50 ng of DNA template/reaction). Products were visualized by primer extension analysis and sequencing gel electrophoresis. The positions of the products for the wild-type MMTV promoter (wtMMTV) and HRE/MMTVΔ are indicated (note that the HRE/MMTVΔ product is 20 bp shorter). (B) Quantification of the transcription signals. Signals were quantified in a phosphoimager (Fuji) and are shown in relative units with wtMMTV control, no H1 and no activator, set to 1. The synergism of PR and NF1 was calculated as: (activity PR + NF1)/(activity PR) + (activity NF1), and is indicated on the top.