Bacterial cells aren't internally compartmentalized with membranes (like eukaryotes). This naturally leads to an image of a homogeneous interior, but bacterial cytoplasm isn't homogeneous. Case in point, the DNA is localized in the nucleoid. If the cell goes through the trouble of putting all its DNA in one spot, having RNA polymerases everywhere would be pretty wasteful (even counterproductive). So, is the more intuitive image of bacteria, with RNAPols everywhere, right? Or are they localized? If so, how?

If species matters, lets primarily talk E. coli.


1 Answer 1


In E. coli most RNA polymerase molecules are bound to DNA, and those that aren't are within easy reach of the DNA.

According to Larry Moran

A typical E. coli cell contains about 5000 molecules of RNA polymerase. When the cells are growing rapidly, 2500 molecules will be bound to genes in transcription complexes. Another 1250 will be in initiation complexes of various sorts and most of the remaining RNA polymerase molecules (1200) will be bound to DNA non-specifically. Only a small number (~50) will be free in the cytoplasm.

The numbers that he quotes for number of molecules of polymerase and proportion that are engaged in transcription are in reasonable agreement with values available at Bionumbers. So it seems that most RNA polymerase molecules will be located in the nucleoid; any molecules that are free in the cytoplasm are within easy reach of finding a DNA binding site since a typical protein can diffuse across an entire E. coli cell in 10 ms. (Bionumbers)


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