| Background |
While overcoming the G1/S checkpoint to commence DNA replication requires cyclin E, and traversing the G2/M checkpoint to initiate mitosis requires cyclin B to be present, cyclin A seems to be required for both S-phase and M-phase A number of studies have described the ability of overexpressed cyclin A to accelerate the G1 to S transition causing DNA replication, and cyclin A antisense DNA can prevent DNA replication Cyclin A availability is apparently the rate-limiting step for entry into mitosis, and cyclin A is required for completion of prophase At late prophase, cyclin A may no longer be necessary as cdc2/cyclinB1 becomes active.
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