PLANT PHYSIOLOGY , Vol 111, Issue 1 285-291, Copyright © 1996 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Inhibitors of Serine/Threonine Phosphoprotein Phosphatases Alter Circadian Properties in Gonyaulax polyedra
J. Comolli, W. Taylor, J. Rehman and J. W. Hastings
Department of Molecular and Cellular Biology, Biological Laboratories, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138
Protein serine/threonine phosphatases were implicated in the regulation of
circadian rhythmicity in the marine dinoflagellate Gonyaulax polyedra based
on the effects of three inhibitors specific for protein phosphatases 1 and
2A (okadaic acid, calyculin A, and cantharidin). Chronic exposure to
okadaic acid resulted in a significant period lenghtening, as measured by
the bioluminescent glow rhythm, whereas cantharidin and calyculin A caused
large phase delays but no persistent effect on period. Short pulses of the
phosphatase inhibitors resulted in phase delays that were greatest near
subjective dawn. Unlike 6-dimethylaminopurine, a protein kinase inhibitor,
okadaic acid, calyculin A, and cantharidin did not block light-induced
phase shifts. The inhibitors tested also increased radiolabeled phosphate
incorporation into Gonyaulax proteins in vivo and blocked protein
phosphatase 1 and 2A activities in Gonyaulax extracts. This study indicates
that protein dephosphorylation catalyzed by protein serine/threonine
phosphatases is necessary for proper functioning of the circadian system.
