Prokaryotic genome organization

Our knowledge of bacterial and phage genome organization and function is considerable. Analysis of these systems is didactic because such an analysis allows us to extrapolate some of the principles of prokaryotic genome organization to eukaryotes. 

A question which needs to be answered is how similar is the prokaryote genome organization and function to that in eukaryotes ... 

With many liter-size bio-reactors the planet would still have looked arid to alien visitors. The Genomic Potential Hypothesis will have all of them make proteins in essentially the same way because it is the only way for making proteins efficiently and repeatedly and to remember forever how it was done. If other routes were possible we would see them today, just like we see differences between prokaryotic and eukaryotic genome organization. Versatile as it is, chemistry is not resourceful enough to provide two independent pathways to life. 

The survival of complex multicellular organisms does not rely greatly on their ability to proliferate rapidly, so their base composition and their nucleotide pool sizes have remained constant over millions of years. E. coli cells can divide every 20 min under optimal conditions, in contrast to eukaryotic cell cycles that take 18 to 24 h. Hence selection pressures such as the rate of nucleobase supply operate on prokaryotic genomes but not on eukaryotic genomes. 

How does prokaryotic genome packaging differ from eukaryotic genome organization ... 

The lac operon in the bacterium Escherichia coli is a well-studied GRN. This prokaryotic gene network has been the subject of numerous reviews it is discussed here primarily to illustrate the various aspects of GRN modeling, starting with the information on genome organization (operon structure) to knowledge on protein-DNA interactions, protein-protein interactions, and the influence of metabolites. 

Fig. 1.23 Sketch of the cross-section of superhelical DNA in a cell. Left DNA is dispersed throughout the cell. Right DNA is confined within the nucleoid phase [255]. Reprinted from C. L. Woldringh and T. Odijk in Organization of the Prokaryotic Genome, R. L. Charlebois Ed.). ASM Press, Amsterdam, Copyright 1999, with permission from ASM Press...

The temporal genome organization of eukaryotes could have evolved from the functional organization of the prokaryotic genome. The temporal sequence of protein synthesis in prokaryotes occurs from a stable, polycistronic template which is determined by the linear sequence of cistrons (Ohtaka and Spiegelman, 1963). For instance, the enzymes for histidine synthesis are in a sequence which corresponds to the linear gene sequence in the histidine operon of Salmonella typhimurium. There is a 20 min period between the appearance of the first and last (tenth) enzymes. The data can be explained on the basis of the successive synthesis of individual mRNA s or on the successive synthesis of a polycistronic message. This... 

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