Physical Structure of the Bacterial Chromosome

I I Electron micrographs of the E. coli chromosome sug-jj gcst a folded circular structure containing about 40-f 100 supercoiled loops (diagrammatically indicated in fig. 25.16). It is believed that the folded structure is held together by an RNA-protein core, although the manner in which this is done is not well understood. The structure is further stabilized because the core forms a complex with positively charged polyamines and certain basic proteins. D. E. Pettijohn and his co-workers have provided evidence of such a core. They first showed that the individual super- 

coli chromosome exists as a circular, folded, supercoiled duplex (a). This can be converted to a partially unfolded structure by brief treatment with RNase (c). There are 50-100 loops in the structure supercoiling may be selectively eliminated from individual loops by single-strand nicking of the DNA within the loop (b). 

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Physical Structure of the Bacterial Chromosome The Genetic Map of Escherichia coli Eukaryotic DNA Is Complexed with Histones Organization of Genes within Eukaryotic... 

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