Cell cycle function of a Medicago sativa A2-type cyclin interacting with a PSTAIRE-type cyclin-dependent kinase and a retinoblastoma protein

Plant J. 2000 Jul;23(1):73-83. doi: 10.1046/j.1365-313x.2000.00794.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cell Cycle*
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Cyclin A / chemistry
  • Cyclin A / metabolism*
  • Cyclin-Dependent Kinases / metabolism*
  • DNA Primers
  • Medicago sativa / cytology
  • Medicago sativa / metabolism*
  • Molecular Sequence Data
  • Protein Binding
  • Retinoblastoma Protein / metabolism*
  • Sequence Homology, Amino Acid
  • Zea mays / metabolism


  • Cyclin A
  • DNA Primers
  • Retinoblastoma Protein
  • Cyclin-Dependent Kinases