Poster: Cell Cycle & Cytokinesis
Abs #
1088: Analysis of the G1/S transition control in re-entering tobacco BY-2 cells
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Presenter: |
Harashima, Hirofumi , h-harasi@bs.aist-nara.ac.jp |
Authors | Harashima, Hirofumi (A) Kawamura, Kazue (A) Sekine, Masami (A) Atsuhiko, Shinmyo (A) | | Affiliations: |
(A): Graduate School of Biological Sciences, Nara Institute of Science and Technology
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Control of the G1/S transition is a crucial regulatory point of commitment to cell division in plants. Plant cell cycle regulators, acting at the G1/S transition, share a high degree of similarity to their animal counterparts. D-type cyclin (CycD) is involved in the integration of environmental stimuli in response to external signals through the formation with the regulatory subunit of cyclin-dependent kinase (CDK) complexes.
We have investigated the regulation of CDKA-associated kinase activity when stationary phase of tobacco BY-2 cells were transferred into a fresh medium. p13suc1-associated proteins containing cyclin/CDKA complexes exhibit kinase activity against histone H1 and tobacco retinoblastoma-related protein. Although histone H1 kinase activity rapidly increased at 6 h with the highest levels reached at 12 h, NtRb1 kinase activity was markedly increased at 8 h. Western analysis revealed that CDKA protein gradually increased up to 24-h, whereas levels of several cyclins were constant, indicating that CDKA kinase activity largely reflects protein abundance of CDKA. However, CDKA protein bound to p13suc1-beads was equivalent level during a 12-h period. This suggests that kinase activity of cyclin/CDKA complexes is regulated at the protein level.
To investigate whether post-translational modification of CDKA was also participated kinase activity, immunoblots were performed with the phosphorylation-specific Thr-161 and Tyr-15 antibodies against animal Cdc2, homolog of CDKA. In contrast to the increase in phosphorylation of Thr-161 during re-entering the cell cycle, no phosphorylation of Tyr-15 is observed, suggesting that CAK (CDK-activating kinase) is most likely involved in modulating CDKA kinase activity through phosphorylation of Thr-161 in CDKA.
