Protein kinase A is required for chromosomal DNA replication

Passage through mitosis resets cells for a new round of chromosomal DNA rep lication [1], In late mitosis, the pre-replication complex - which includes the origin recognition complex (ORC), Cdc6 and the minichromosome maintena nce (MCM) proteins - binds chromatin as a pre-requisite for DNA replication . S-phase promoting cyclin-dependent kinases (Cdks) and the kinase Dbf4-Cdc 7 then act to initiate replication. Before the onset of replication Cdc6 di ssociates from chromatin. S-phase and M-phase Cdks block the formation of a new pre-replication complex, preventing DNA over-replication during the S, G2 and M phases of the cell cycle [1]. The nuclear membrane also contribut es to limit genome replication to once per cell cycle [2], Thus, at the end of M phase, nuclear membrane breakdown and the collapse of Cdk activity re set cells for a new round of chromosomal replication. We showed previously that protein kinase A (PKA) activity oscillates during the cell cycle in Xe nopus egg extracts, peaking in late mitosis, The oscillations are induced b y the M-phase-promoting Cdk [3,4], Here, we found that PKA oscillation was required for the following phase of DNA replication. PKA activity was neede d from mitosis exit to the formation of the nuclear envelope. PKA was not r equired for the assembly of ORC2, Cdc6 and MCM3 onto chromatin. Inhibition of PKA activity, however, blocked the release of Cdc6 from chromatin and su bsequent DNA replication. These data suggest that PKA activation in late M phase is required for the following S phase.