High Molecular Weight Protein is Presumably Essential for the Circadian Clock

Many functions in living organisms are known to oscillate. The frequency spectrum ranges from fractions of a second up to at least a year (1). Among these oscillations, those with a period of about 24 hours, the so-called circadian rhythms, play a major role (2, 3). For a number of years, the extent to which oscillations in living systems can be compared with those occurring in physico-chemical systems has been discussed (4). A critical question is whether the insight gained in recent years into the mechanism of physico-chemical oscillations can be of help in understanding oscillations in living systems. Before answering this question, one should recall that a basic difference between the oscillations of physico-chemical and living systems is that living systems have been, and still are, subjected to evolution. This implies that the oscillations under discussion should have a selective advantage. In contrast to other oscillations in livings systems, most circadian rhythms allow a convincing answer to be given to this question (3, 5).