Escherichia coli chromosome size

Most of the DNA of animal cells is found in the nucleus, where DNA is the major constituent of the chromosomes. On the other hand, most of the RNA is located in the cytoplasm. Nuclear DNA exists as a thin, double helix only 2 nm wide. The double helix is folded and complexed with protein to form chromosomal strands approxim-ately 100 to 200 nm in diameter. Each chromosome contains a single DNA duplex. The human chromosomes vary in size the smallest contains approximately 4.6 X 10 base pairs of DNA, and the largest 2.4 X 10 base pairs. In contrast, the Escherichia coli chromosome has 4.5 x 106 base pairs. The DNA of die chromosomes is tightly packed and associated with both histone and nonhistone proteins. 

Donachie WD, Blakely GW (2003) Coupling the initiation of chromosome replication to cell size in Escherichia coli. Curr Opin Microbiol 6 146-150 Doolittle WF, Sapienza C (1980) Selfish genes, the phenotype paradigm and genome evolution. Nature 284 601-603... 

The most highly developed genetic map is that of Escherichia coli K12, and it has recently been augmented with coarse [10] and fine [11] restriction maps. As the most nearly complete genetic map it can give us clues to structural features which may be functionally important, especially since some data exist on the effects of chromosomal rearrangements. This makes it a natural reference to which other maps of similar-sized genomes can be compared. 

Pl-derived artificial chromosome. (PAC). One type of vector used to clone DNA fragments (100- to 300-kb insert size average, 150 kb) in Escherichia coli cells. Based on bacteriophage (a virus) PI genome. 

Types of DNA Found in Bacterial Cells. Most of the DNA in a bacterial cell is contained on one large DNA molecule known as the chromosome or genophore. In Escherichia coli the chromosome is about 3.7x10 base pairs in size and can encode about 3000 genes. 

Fig. C2.7 Electron microscope picture of bacterial DNA partially released from the cell (bacteria E. coli) upon gentle breaking of the cell outer membrane (see Sections 2.4, 6.3 and 9.12). The figure illustrates how dense is the DNA packing under native conditions we see that even spilled out DNA is rather dense and tangled, we can therefore imagine how dense it was while still inside the cell. The scale bar in the image corresponds to 1 mm, or 1,000 nm — about the size of the cell. The figure is reproduced with permission from the classical paper Ruth Kavenoff and B.C. Bowen, "Electron Microscopy of Membrane-Free Folded Chromosomes from Escherichia Coli , Chromosoma, V. 59, n. 2, pp. 89— 101, 1976.

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