Figure 2.

The upregulation of frq mRNA simulates inaccurate PRCs in response to light. (A) The PRC of N. crassa to 5-min light pulses with an intensity of 1750 lux (42) mainly consists of three parts: a dead zone in the subjective day (CT6–CT12), a delay zone in the early subjective night (CT12–CT22), and an advance zone in the late subjective night continuing into the early subjective morning (CT22–CT6). Here, CT0 is the time when Neurospora has been in constant darkness for ∼11 h (one half of the free-running period) after being shifted from constant light to constant darkness. Red triangles represent data from (42), and the contour of the shaded area represents the optimal PRC shape traversed by this data. (B) PRCs simulated with an additive pulse of frq transcription for 5 min do not match the experimental data (Fig. 2A). The magnitude of a pulse increasing the rate of frq mRNA (i.e., c_f in Eq. 3) was chosen so that the magnitudes of the resulting phase shifts were similar to the experimental data: 1, 12, and 45(arbitrary unit hour) ⁻¹ in the simple model, Dovzhenok model, and Tseng model, respectively (see Materials and Methods for details). (C) The simulated PRCs with a multiplicative pulse of frq transcription for 5 min do not match the experimental data (Fig. 2A). The magnitude of a pulse that increases the maximal transcriptional rate of the Hill function was chosen so that the magnitudes of the resulting phase shifts were similar to the experimental data (Fig. 2A): α_m is increased from 5.9 to 80.9 h⁻¹ in the simple model, k₁ from 1.8 to 71.8 h⁻¹ in the Dovzhenok model (68), and k₀₁ from 7.3 to 207.3 h⁻¹ in the Tseng model (46). To see this figure in color, go online.