Tyrosine kinase regulation of a molluscan circadian clock.

On a formal level the clocks regulating circadian and cell division cycles are related in that both have been modeled as limit cycle oscillations (Science, 211 (1981) 1002-1013; Brain Res., 504 (1989) 211-215; Proc. Natl. Acad. Sci. USA, 88 (1991) 7328-7332). Furthermore, in several organisms each clock system is able to modulate the other (Science, 211 (1981) 1002-1013). However, in spite of the similarities at the formal level, and the connections at the physiological level, no common cellular elements have been identified linking the two processes. In the current series of experiments we show that one key element of cell cycle regulation, tyrosine phosphorylation/dephosphorylation is intimately associated with circadian rhythm generation in the eye of the marine snail, Bulla gouldiana. The importance of tyrosine kinase activity in the generation of circadian rhythms provides a possible point of similarity between the fundamental biochemical mechanisms underlying both circadian and cell cycle clocks.