| Comments |
Early electron micrographs showed E. coli nucleoids obtained from lysed cells with large DNA loops emanating from a central core. These loops were inferred to be interwound, suggesting the presence of supercoiling in vivo (Kavenoff and Bowen, 1976). Dynamic, independent, superhelical domains with variable sizes and positioning of their boundaries were later demonstrated using genetic methods. Initially, it was believed that these domains were up to several hundred kb in size, but more recent estimates indicate that these domains are probably closer to 10 to 20 kb in size. Thus, the E. coli chromosome may possess as many as ~ 400 independently supercoiled domains. For 30 to 200 DNA physical domains see Moselio Schaechter, John L. Ingraham, Frederick C. Neidhardt, Microbe, 2006 ASM Press 1 edition p.140 1st paragraph. |