Model for the circadian clock of N. crassa . Model for the circadian clock of N. crassa. A. FRQ mRNA (M) is translated into protein (Pc) in the cytoplasm and then transported into the nucleus (Pn) where it represses the transcription of FRQ. Light entrains the model by increasing the transcription rate. B. Simulated time series showing sparse samples as symbols: M (circles), Pc (squares), and Pn (triangles) and the finely-sampled stochastic simulation from which they are selected.