title: Cyclin A recruits p33cdk2 to the cellular transcription factor DRTF1.
abstract: Cyclins are regulatory molecules that undergo periodic accumulation and destruction during each cell cycle. By activating p34cdc2 and related kinase subunits they control important events required for normal cell cycle progression. Cyclin A, for example, regulates at least two distinct kinase subunits, the mitotic kinase subunit p34cdc2 and related subunit p33cdk2, and is widely believed to be necessary for progression through S phase. However, cyclin A also forms a stable complex with the cellular transcription factor DRTF1 and thus may perform other functions during S phase. DRTF1, in addition, associates with the tumour suppressor retinoblastoma (Rb) gene product and the Rb-related protein p107. We now show, using biologically active fusion proteins, that cyclin A can direct the binding of the cdc2-like kinase subunit, p33cdk2, to complexed DRTF1, containing either Rb or p107, as well as activate its histone H1 kinase activity. Cyclin A cannot, however, direct p34cdc2 to the DRTF1 complex and we present evidence suggesting that the stability of the cyclin A-p33cdk2 complex is influenced by DRTF1 or an associated protein. Cyclin A, therefore, serves as an activating and targeting subunit of p33cdk2. The ability of cyclin A to activate and recruit p33cdk2 to DRTF1 may play an important role in regulating cell cycle progression and moreover defines a mechanism for coupling cell-cycle events to transcriptional initiation.
authors.affiliation: Laboratory of Eukaryotic Molecular Genetics, MRC National Institute for Medical Research, Mill Hill, London, UK.
authors.forename: L R
authors.initials: LR
authors.lastname: Bandara
authors.forename: J P
authors.initials: JP
authors.lastname: Adamczewski
authors.forename: M
authors.initials: M
authors.lastname: Zamanian
authors.forename: R Y
authors.initials: RY
authors.lastname: Poon
authors.forename: T
authors.initials: T
authors.lastname: Hunt
authors.forename: N B
authors.initials: NB
authors.lastname: Thangue
mesh_terms: D001483:Base Sequence; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D016213:Cyclins / Q000502:physiology*; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D008969:Molecular Sequence Data; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases