Themet1 mutation inChlamydomonas reinhardtii causes arrest at mitotic metaphase with persisting p34cdc2-like H1 histone kinase activity that can promote mitosis when injected into higher-plant cells

Abstract

Summary.The metl mutation in Chlamydomonas reinhardtii causes metaphase arrest. Arrested cells have disassembled cortical microtubules, a fully assembled spindle, condensed and aligned metaphase chromosomes and abundant mitotic phosphoproteins recognised by MPM-2 antibody in the nuclear region. Protein purified by affinity for the mitotic protein p 13 s~cl contains p34Cd~2-1ike H 1 histone kinase activity at times when control cells have inactivated this enzyme. The active enzyme, when microinjected into Tradescantia stamen hair cells, accelerated progress through prophase to normal completion of mitosis, indicating that the mutation did not disable the mitotic Cdc2 protein kinase enzyme complex. The mutation prevented the normal lowering of this kinase activity that accompanies anaphase. A defect at time of mitosis rather than earlier in the cycle was indicated by temperature shifting of synchronous cells, which identified the earliest faulty progress as occurring near the beginning of mitosis and the time at which the essential function is completed near the end of mitosis. The metl gene mapped approximately 33 cM from ery-2 and extended the known limits of the linkage group XIV.

CHLAMYDOMONAS AS A MODEL ORGANISM

“…New conditional cell cycle mutants have been isolated by John and colleagues (203,242), and the old mutants have been subjected to further study as well. The results now emerging indicate that Chlamydomonas has great potential as a system for genetic analysis of cell cycle control.…”

The effect of ICK1, a plant cyclin-dependent kinase inhibitor, on mitosis in living plant cells

“…Their rate of mitosis is well documented (e.g. Hepler 1985;Wolniak and Bart 1985), and these cells have been of proven utility in the study of the regulation and facilitation of plant mitosis following microinjection of cell-cycle proteins (Hush et al 1996;Wu et al 1997) and cytoskeletal probes (Zhang et al 1990;Cleary et al 1992). We show that the addition of ICK1 to prophase and early prometaphase cells results in a load-and injection time-dependent increase in the metaphase transit time, demonstrating an in vivo effect of ICK on the cell cycle and the continuing importance of high CDK activity in mitotic progression.…”