General Chromosome Structure
The DNA in eukaryotic cells is largely contained in nucleosomes. Sets of these nucleosomes form solenoids, and the solenoids wrap together to form yet a larger structure. Within all this compaction, the DNA must remain accessible to regulatory proteins, to RNA polymerase for tran-scription, to DNA repair enzymes, and to any other proteins that have a need for access to the DNA. If a nucleosome is bound to the promoter for a given gene, RNA polymerase would be denied access, and neces-sary transcription would not occur. Are there any special mechanisms that either remove nucleosomes from important regions of DNA or which prevent their binding there in the first place? The next section shows how nucleosome positions on DNA can be determined.