FLP Recombinase and Yeast DNA Replication: Solving the 2 micron Plasmid Problem

[whamola411]

This problem talks about the 2 micron plasmid of s. cerivisiae. The yeast cell cycle has a limited time during which initiation of DNA replication can occur. This initiation window is too short to allow the plasmid to undergo several serial replications. The flp system provides a mechanism whereby the copy number of the plasmid can be rapidly increased with one replication initiation event. Show that this is so by observing what happens if flp recombination occurs shortly after replication has begun. Specifically, follow the consequences of recombination between one flp site that has just been replicated and a second site that is still ahead of the DNA replication fork. Look at what happens as the fork advances. Describe this. How does it solve the replication initiation problem described above

I am pretty lost on this. My only idea is that if recombination occurs just after replication it can utilize a rolling circle mechanism. Otherwise, if it starts ahead of the fork, it wouldn't. Thanks for your help!

 

[Nino MMP]

The Flp system works by using a specific type of recombination called site-specific recombination. This process involves the recognition and exchange of two specific sequences (known as flp sites) located on the same plasmid molecule. When replication occurs, the two flp sites are replicated along with the plasmid's DNA. As the replication fork advances, one of the flp sites is copied and the other one remains ahead of the fork. When the two flp sites come into contact, they recombine, creating a circle of DNA that can then be replicated again. By replicating the plasmid in this way, the copy number of the plasmid can be rapidly increased with one replication initiation event, thus solving the problem of the limited time during which initiation of DNA replication can occur.