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An Inhibitor of Protein Phosphorylation Stops the Circadian Oscillator and Blocks Light-Induced Phase Shifting in Gonyaulax polyedra

Department of Cellular and Molecular Biology, Harvard University, 16 Divinity Avenue. Cambridge, Massachusetts 02138

Walter Taylor

Department of Cellular and Molecular Biology, Harvard University, 16 Divinity Avenue. Cambridge, Massachusetts 02138

J.W. Hastings

Department of Cellular and Molecular Biology, Harvard University, 16 Divinity Avenue. Cambridge, Massachusetts 02138

The expression of circadian rhythmicity in Gonyaulax polyedra is strikingly altered by an inhibitor of protein phosphorylation. The effects of 6-dimethylaminopurine (6-DMAP), known to reversibly block cell division in many systems through inhibition of protein kinase activity, are described here for Gonyaulax. Its action appears to be exclusively tonic in nature; in cells continuously exposed, the period is lengthened in a concentration-dependent fashion. Shorter treatments at a higher concentra tion of 6-DMAP (5 mM) apparently stop the circadian oscillator, but reversibly so, since the rhythm resumes after drug removal with a phase delay approximately equal to the duration of the treatment. Pulses of the inhibitor are effective in causing phase delays at all times of the circadian cycle. In addition, 6-DMAP completely blocks light-induced phase advances and is effective in inhibiting many Gonyaulax protein kinases in vitro.

Key Words: protein kinase • 6-dimethylaminopurine • 6-DMAP • phosphorylation • dinoflagellate • circadian • Gonyaulax • phase shifting

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