Question

Your friend works in a lab that studies origin licensing. He is particularly interested in the pre-replicative complex (pre-RC) and has isolated a temperature-sensitive yeast mutant that does not seem to assemble the pre-RC at the origins of replication. However, he has gotten into an argument with a new student in the lab. The student thinks that this yeast mutant will arrest in late mitosis or early G₁, because that is when the pre-RC is normally assembled. Your friend disagrees. Who is right, and why?

Answer 1

The pre-replicative complex is an assembly of proteins at origin of replication where DNA synthesis begins. The complex is assembled during the M to G1 phase transition of the cell division cycle, and is inactivated during the S-phase. A second preRC cannot be assembled until mitosis is completed and a nuclear membrane is present. The formation of preRC begins with assembly of an origin of replication complex composed of the subunits Orc1 through Orc6. Cdc6 proteins then bind to the ORC, and subsequent binding of other proteins like Mcm 2 to 7, forms the preRC. A DNA binding protein called Noc3 is highly required for this complex to form.

Therefore, the given statement is wrong.