Bacterial Chromosome Structure
The structure of the bacterial chromosome can be considered at several different levels. By analogy with protein structure one can potentially describe: (a) a one-dimensional representation consisting of the nucleotide sequence of the entire circular DNA of the chromosome, or there can be a less molecular description of the linear sequence of genes; (b) a two-dimensional description of the folds that are placed in the circular DNA; (c) a three-dimensional picture of, the chromosomal DNA that includes the writhing and supercoiling of the axis of the DNA double helix in the chromosome. However, the analogy with protein structure should not be carried too far, because the three-dimensional structure of the chromosome appears to be dynamic in its organization and its structural fluctuations may go beyond the kinds of statistical perturbations expected in proteins. One indication of these fluctuations in three-dimensional structure is that the shape of the bacterial nucleoid is irregular and varies in different cells in the same culture. Furthermore, it is known that the average size and shape of the nucleoid change when cells are grown in different media or under different conditions (see for example, Woldringh and Nanninga 1985). This brief review will focus primarily on the last two descriptions, i.e., the two- and three- dimensional structures and their stabilizing protein-DNA interactions. The reader is referred to earlier reviews that also discuss the structure of the chromosome visualized by different microscopic techniques (Woldringh and Nanninga 1985; Pettijohn and Sinden 1985; Bjornsti et al. 1986) and other features of the structure of bacterial chromosomes as well (Kleppe et al. 1979; Drlica and Rouviere-Yaniv 1987; Pettijohn 1988).
KeywordsRecombination Bromide Bacillus Lution Ethidium
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