BIO 320 Lecture Notes - Lecture 32: Dna Replication Factor Cdt1, Cdc6, Geminin
Document Summary
Initiation of chromosomal dna replication (i. e. , g1 to s transition) occurs at multiple sites (replication origins) in eukaryotes. This process requires the loading of a specific set of proteins (including dna polymerase and dna helicase) at each replication origin. Certain proteins at each replication origin are then phosphorylated and activated by s-cdk (and another kinase). Each chromosome is replicated once and only once per cell cycle. Orc is bound to replication origins through the entire cell cycle. S-cdk and m-cdk each can phosphorylate cdc6, causing its poly- ubiquitination and degradation. Thus, cdc6 begins to accumulate only after inactivation of m-cdk during late. Apc/c causes degradation of an inhibitor (geminin) of cdt1 until late g1 (when apc/c becomes inactive, see later slide). Hence, cdc6 and cdt1 can function as loading factors for the mcm dna helicase only in late m and early g1.
