Studies on the Folded Chromosome of Escherichia coli

Abstract

The DNA of E. coli, a double-stranded closed ring with a length of more than one millimeter (Cairns, 1963), is packaged inside the cell into nuclear bodies about one µm in diameter. This highly folded DNA molecule must be constrained into a fraction of the cell volume (Ryter, 1968) in the absence of a nuclear membrane. The DNA packaging probably is not random, as evidenced by the successful segregation (apparently without entanglement) of the daughter chromosomes. The folding of the DNA also does not interfere with DNA replication and transcription; on the contrary, the DNA packing is such that any bacterial gene is accessible for transcription at any given time. It appears that the DNA must be folded inside the cell according to some, as yet unknown, regular rules.