title: Robust reconstitution of active cell-cycle control complexes from co-expressed proteins in bacteria.
abstract: BACKGROUND
  Cell proliferation is an important determinant of plant growth and development. In addition, modulation of cell-division rate is an important mechanism of plant plasticity and is key in adapting of plants to environmental conditions. One of the greatest challenges in understanding the cell cycle of flowering plants is the large families of CDKs and cyclins that have the potential to form many different complexes. However, it is largely unclear which complexes are active. In addition, there are many CDK- and cyclin-related proteins whose biological role is still unclear, i.e. whether they have indeed enzymatic activity. Thus, a biochemical characterization of these proteins is of key importance for the understanding of their function.
  
  
  RESULTS
  Here we present a straightforward system to systematically express and purify active CDK-cyclin complexes from E. coli extracts. Our method relies on the concomitant production of a CDK activating kinase, which catalyzes the T-loop phosphorylation necessary for kinase activity. Taking the examples of the G1-phase cyclin CYCLIN D3;1 (CYCD3;1), the mitotic cyclin CYCLIN B1;2 (CYCB1;2) and the atypical meiotic cyclin SOLO DANCERS (SDS) in conjunction with A-, B1- and B2-type CDKs, we show that different CDKs can interact with various cyclins in vitro but only a few specific complexes have high levels of kinase activity.
  
  
  CONCLUSIONS
  Our work shows that both the cyclin as well as the CDK partner contribute to substrate specificity in plants. These findings refine the interaction networks in cell-cycle control and pinpoint to particular complexes for modulating cell proliferation activity in breeding.
authors: Department of Molecular Mechanisms of Phenotypic Plasticity, Institut de Biologie Moléculaire des Plantes du CNRS, IBMP-CNRS - UPR2357, Université de Strasbourg, 12, rue du Général Zimmer, F-67084, Strasbourg Cedex, France. Arp.Schnittger@ibmp-cnrs.unistra.fr.
authors: Hirofumi
authors: H
authors: Harashima
authors: Arp
authors: A
authors: Schnittger