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When a prokaryote undergoes binary fission, how are the non-DNA macromolecules distributed between the two daughter cells? This is motivated by comments on a previous question and a G+ discussion. I am primarily interested in explicit mathematical models.


Naive model

For DNA, each copy is attached to a different part of the cell membrane, to ensure each of the daughters receives a copy. As far as I understand, there isn't such specific mechanism in place for other macromolecules. If we are allowed to assume that non-DNA macromolecules are distributed uniformly through the parent cell than this would mean the two daughter cells would receive half the proteins within statistical fluctuation. This has a specific meaning: if there are $N$ molecules of type A in the parent, then the difference in number of type A molecules in the two daughters after fission will be on the order of $\sqrt{N}$.

However, this model might be wrong. For instance, as the new cell-wall is being formed it could have in it specific pumps that either balance the protein levels below chance (producing an average difference lower than $\sqrt{N}$) or to create asymmetries higher than chance. Altenrnatively, the initial distribution of macromolecules in the parent could be far from symmetric for some other reasons. Which is the case?

If the naive model is correct, is there experimental evidence explicitly showing this?

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blog post discussion of how the cytoplasm can't just be modeled as a homogeneous mixture. –  Artem Kaznatcheev Mar 20 '13 at 17:18
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1 Answer

Many years ago I worked in the field of bacterial chemotaxis, and your question brought this paper to mind:

JL Spudich & DE Koshland Jr. (1976) Non-genetic individuality: chance in the single cell. Nature 262:467-471.

The authors report an analysis of the chemotactic behaviour of individual bacterial cells from a single homogeneous culture. They find marked differences between individuals, and their favoured model is what they refer to as a Poissonian variation in the inheritance of key proteins that are present in small numbers.

According to ISI Web of Science this paper has been cited 241 times - presumably at least some of those papers might be about other more recent examples of this type of phenomenon.

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This is a great starting point, thank you! I will search forward from here. –  Artem Kaznatcheev Sep 1 '12 at 20:43
    
Incidentally, as a counter example, there is a lot of good work showing that mRNAs are actively moved around during bud formation in yeast. This paper is probably a good place to start (in the middle of the story!). K. A. Shepard et al. (2003) Widespread cytoplasmic mRNA transport in yeast: Identification of 22 bud-localized transcripts using DNA microarray analysis. Proc Natl Acad Sci U S A. 100:11429–11434. doi: 10.1073/pnas.2033246100 –  Alan Boyd Sep 2 '12 at 7:34
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