The molecular basis of the Neurospora clock

Circadian rhythms represents a nearly universal mode of cellular and organismal regulation among the eukaryotes. The common characteristics of biological clocks are shared throughout the breadth of phylogeny, and this shared set of features may reflect a shared molecular organization. It is clear that the molecular feedback loop that describes the central pacemaker mechanism will be found at the level of the cell in all organisms, so that molecularly simple systems may be useful for providing insights into more complex systems. The filamentous fungus Neurospora crassa is a well characterized genetic and biochemical system with a widely studied and well characterized circadian clock. Building on a strong genetic background, the mRNA and protein products of the frequency ( frq ) locus are now known to be components of the feedback loop that constitutes the pacemaking mechanism. The circadian oscillator in Neurospora can be described as an autoregulatory negative feedback loop wherein the products of the frq locus regulate themselves. In other work, the molecular cloning of genes under daily regulation by the clock is beginning to show the pathways through which clocks control gene expression, and how this aspect of regulation interfaces with acute responses to the environment.