Re: What in detail is the dispersive model of DNA replication?

Hello!

I searched on the internet for a picture of a model of dispersive DNA replication and I found one at http://www.accessexcellence.org/AB/GG/possible.html. You'll notice that here the new "dispersive" strand contains stretches of old DNA on both strands of the helix, interspersed by stretches of new DNA on both strands of the helix. Since there is no obvious template for the stretches of all new bases, it would be fairly complicated to generate these regions. Possibly, one strand could be used as template, then the old DNA could be deleted and a second strand could be synthesized, this time using the newly replicated strand as template. Such a mechanism is analogous to gene conversion as well as the repair mechanism for some DNA lesions. However, it would necessarily have to be much more complicated and involved than our current understanding of semi-conservative replication. For example, thee would have to be a signal for which areas are created wholly anew at each round of replication. Are there some regions that are always old or new, and is there a way for the cell to tell how old the DNA is and when it's necessary to create new DNA? There would have to be some sort of "marking" (e.g. methylation) on the bases to distinguish old DNA from newly synthesized DNA.

On the other hand, it's also possible that one strand is used as template in some parts of the chromosome, while the other strand is used as a template elsewhere. This model would be essentially semi-conservative, using the same method of priming and 5' to 3' extension that we are familiar with, but only in stretches on a given molecule. As well, there would have to be some sort of signal indicating to "switch" the strand used as template.

I cannot find any reference to any scientist who supported the dispersive hypothesis or whether a detailed model had been thought out before 1958. I believe the consensus is that it was just a theoretical hypothesis -- a brainstorming possibility if you will. So you (and your students) are on your own with coming up with possible models and mechanisms :-)

Previous MadSci posts related to models of DNA replication:

963264796.Sh
857086400.Ge 876240225.Sh

Hope that helped,

Sanjida