The organization of the DNA that is achieved by the nucleosome cannot fully explain the packaging of DNA observed in the cell nucleus. Further compaction of chromatin into the cell nucleus is necessary, but it is not yet well understood. The current understanding is that repeating nucleosomes with intervening "linker" DNA form a "10-nm-fiber", described as "beads on a string", and have a packing ratio of about five to ten. A chain of nucleosomes can be arranged in a "30 nm fiber", a compacted structure with a packing ratio of ~50 and whose formation is dependent on the presence of the H1 histone.