Question

In eukaryotes, what is meant by the term DNA replication licensing? How does the process occur?

Short answer

DNA replication licensing in eukaryotes refers to the process that ensures DNA replication occurs only once per cell cycle. It involves the formation of a pre-replication complex at the replication origin during the G1 phase of the cell cycle. The main components include the Origin Recognition Complex (ORC), Cdc6, Cdt1, and the Mcm2-7 complex. The degradation or removal of Cdc6 and Cdt1 prevents re-replication until the next cell cycle.

Step-by-step solution

Defining DNA replication licensing

'DNA replication licensing' is a term used in cell biology to describe the method of controlling DNA replication to ensure that it only occurs once in a single cell cycle. The licensing process sets up the necessary machinery for DNA replication to happen and ensures that it doesn't reoccur until the cell is ready to divide.

Key Proteins Involved in Licensing

The main proteins involved in the licensing process are 'licensing factors' also known as pre-replication complexes (pre-RCs). The major components of a pre-RC include Origin Recognition Complex (ORC), Cdc6, Cdt1, and the Mcm2-7 helicase complex.

Describing the Licensing Process

The process starts in the G1 phase of the cell cycle when the ORC identifies and attaches to the DNA replication origins. Cdc6 and Cdt1 then recruit and load the Mcm2-7 complex onto the replication origin, forming the pre-RC and thus 'licensing' the origin for replication. During the S phase, additional factors activate the Mcm2-7 complex, initiating the process of DNA replication. To prevent re-replication, Cdc6 and Cdt1 are either degraded or exported out of the nucleus during the S phase and do not return until the next G1 phase.