Early events in DNA replication require cyclin E and are blocked by p21CIP1.
Using immunodepletion of cyclin E and the inhibitor protein p21WAF/CIP1, we demonstrate that the cyclin E protein, in association with Cdk2, is required for the elongation phase of replication on single-stranded substrates. Although cyclin E/Cdk2 is likely to be the major target by which p21 inhibits the initiation of sperm DNA replication, p21 can inhibit single-stranded replication through a mechanism dependent on PCNA. While the cyclin E/Cdk2 complex appears to have a role in the initiation of DNA replication, another Cdk kinase, possibly cyclin A/Cdk, may be involved in a later step controlling the switch from initiation to elongation. The provision of a large maternal pool of cyclin E protein shows that regulators of replication are constitutively present, which explains the lack of a protein synthesis requirement for replication in the early embryonic cell cycle.
Jackson
P K
PK
Harvard Medical School, Department of Cell Biology, Boston, Massachusetts 02115, USA.
Chevalier
S
S
Philippe
M
M
Kirschner
M W
MW
D000595:Amino Acid Sequence; D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000276:immunology / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects / Q000502:physiology*; D004277:DNA, Single-Stranded / Q000378:metabolism; D005260:Female; D005656:Fungal Proteins / Q000276:immunology / Q000378:metabolism; D008297:Male; D008938:Mitosis / Q000502:physiology*; D008969:Molecular Sequence Data; D010063:Ovum; D011233:Precipitin Tests; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins; D013094:Spermatozoa; D014981:Xenopus; D029867:Xenopus Proteins
D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004277:DNA, Single-Stranded; D005656:Fungal Proteins; D018809:Proliferating Cell Nuclear Antigen; D029702:Schizosaccharomyces pombe Proteins; C051655:Suc1 protein, S pombe; D029867:Xenopus Proteins; D016590:Aphidicolin; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases