Competition between transcription complex assembly and chromatin assembly on replicating DNA.

We have used a Xenopus egg extract to show that a competition exists between the assembly of transcription complexes and nucleosomes on replicating 5S DNA. This competition results in the establishment of a transcriptionally repressed state for 5S DNA that is dependent on core histones but not on the precise positioning of the cores. The repression is selective, since satellite I DNA is not significantly repressed under these conditions. We demonstrate that the efficiency of chromatin assembly compared with transcription complex assembly is an important variable in determining gene activity.