Cell cycle function of a Medicago sativa A2-type cyclin interacting with a PSTAIRE-type cyclin-dependent kinase and a retinoblastoma protein.
In plants multiple A-type cyclins with distinct expression patterns have been isolated and classified into three subgroups (A1-A3), while in animal somatic cells a single type of cyclin A is required for cell-cycle regulation from the S to M phases. We studied the function of an A2-type cyclin from Medicago sativa (Medsa;cycA2) which, in contrast to animal and most plant A-type cyclins, was expressed in all phases of the cell cycle. Using synchronized alfalfa cell cultures and anti-Medsa;CycA2 polyclonal antibodies, we showed that while the mRNA level increased steadily from the late G1 to the G2-M phase, the protein level after a rapid increase in S-phase reached a plateau during the G2 phase. In the yeast two-hybrid system, the Medsa;CycA2 protein interacted with the PSTAIRE-motif-containing cyclin-dependent kinase Cdc2MsA and with the maize retinoblastoma protein. Unexpectedly, the CycA2-associated kinase activity was biphasic: a first activity peak occurred in the S phase while the major one occurred during the G2/M transition, with no apparent dependence upon the actual levels of the Medsa;CycA2 and Cdc2MsA proteins. Immunohistological localization of the cyclin A2 protein by immunofluorescence and immunogold labelling revealed the presence of Medsa;CycA2 in the nucleus of the interphase and prophase cells, while it was undetectable thereafter during mitosis. Together these data suggest that Medsa;CycA2 plays a role both in the S phase and at the G2/M transition.
Institut des Sciences Végétales, CNRS UPR 40, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
F
F
Roudier
E
E
Fedorova
J
J
Györgyey
A
A
Feher
S
S
Brown
A
A
Kondorosi
E
E
Kondorosi
D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D019925:Cyclin A / Q000737:chemistry / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D017931:DNA Primers; D000455:Medicago sativa / Q000166:cytology / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D016160:Retinoblastoma Protein / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000378:metabolism
D019925:Cyclin A; D017931:DNA Primers; D016160:Retinoblastoma Protein; D018844:Cyclin-Dependent Kinases