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Replication of linear plasmids in bacteria

Published on January 31, 2024   45 min

A selection of talks on Microbiology

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The title of this presentation is Replication of Linear Plasmids in Bacteria.
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Let's begin our discussion with a look at the distribution of linear DNA in the bacterial world. This figure shows a tree of relatedness for bacterial phyla, in which phyla have linear replicons. Two things are immediately obvious from this tree. First, a few bacterial phyla carry linear DNA. Second, the ones that do are not closely related. Linear DNA has been found in protobacteria, actinobacteria, and spirochetes. Three phyla that are evolutionarily distant from each other. The observed linear DNA has been found in the form of bacterial chromosomes, plasmids and Phages. The reasons why linear DNA in bacteria is not a common occurrence is discussed in the next slide.
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Most bacterial plasmids are circular molecules. This simplifies the DNA replication process. With linear DNA molecules, we encounter what has been referred to as the end replication problem. This was first noted by James Watson in the early 1970s. The problem results from the fact all DNA polymerases require a primer to initiate DNA synthesis. As shown in this illustration, when synthesis is complete on the lagging strand, and the RNA primer at the five prime end of the newly replicated strand is removed, we are left with a gap. This gap cannot be filled in de novo by a DNA polymerase, and we are left with unreplicated DNA at the ends of the lagging strand of linear DNA molecules.

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