The peptide PIN changes the timing of transitory burst activation of timer-ATPase TIME in accordance with diapause development in eggs of the silkworm, Bombyx mori

TIME is an ATPase that measures a time interval by exhibiting transitory burst activation in eggs of the silkworm, Bombyx mori L. PIN is a peptide that regulates the time measurement of TIME. To address the mode of action of PIN, interactions between TIME and PIN were investigated. First, TIME was mixed with PIN for various periods (days) at 25 °C. The longer TIME was mixed with PIN, the later the transitory burst activation of TIME ATPase activity occurred, while no such delay occurred at 5 °C. Second, the capacity of PIN to bind with TIME was measured at the two temperatures by fluorescence polarization. The binding interaction was much tighter (nearly 1000 times) at 25 °C than that at 4 °C. Because the log EC50 (in nM) at 4 °C was about 7, PIN must dissociate from TIME at low temperatures at the physiological concentration of TIME in eggs. Thus, TIME appears to be restructured into a time-measuring conformation by PIN at the high temperatures of summer, whereas the TIME–PIN complex would dissociate at the low temperatures of winter. This dissociation acts as the preliminary cue for the ATPase activity burst of TIME, which in turn causes the completion of diapause development and initiates new developmental programs.