Our teacher said that Bacillus subtilis has an asymmetrical replication fork.

I know that this happens only in some strain of the bacteria . She asked us to find an explication for this mechanism , but all that I was able to find is that the chromosome is more compacted in some areas, therefore it slows the replication .

Are there other reasons?

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    $\begingroup$ Are you sure that your teacher was not referring to asymmetric replication as in asymmetric cell division? B. subtilis undergoes asymmetric cell division, whereby the two daughter cells have different fates, in this case during sporulation. Are you at a college level? If so, then there is this article. It might be a little too advanced if you are not at the college level. If it was in fact replication, then it is likely that she wants you to explain leading and lagging strand synthesis. $\endgroup$
    – AMR
    Oct 30 '15 at 18:35

The replication fork itself is always asymmetric. This is true for all organisms and is due to the fact that DNA polymerases can only add nucleic acids to the 3'-OH end of DNA. This leads to different mechanisms for the replication of the so called leading and lagging strands. You can find more details on wikipedia https://en.wikipedia.org/wiki/DNA_replication

Most Bacteria have circular chromosomes that they usually replicate using two replication forks. Both forks start from the origin of replication and progress in opposite directions to meet at the replication terminus which is opposite to the replication origin on the circular chromosome. Each replication fork replicates about half of the chromosome. We talk about the left replicore and the right replicore. I assume that your teacher was referring not asymmetry in the replication fork itself, but to asymmetry in the size of the replicores. In B. subtilis the left replicore is 196 kb longer than the right replicore (J Bacteriol. 1993 Feb; 175(3): 741–749.). I do not know whether there is any evolutionary explanation for this, but mechanistically it is caused by the fact that the terminus of replication is not placed opposite to the origin of replication on the circular chromosome.


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