Figure 3. Transcription Is Discontinuous

(A) Multiple pulses of dscA transcription. The central cell initially transcribes for 5 frames, then is inactive for 3 frames before reinitiating and expressing for a further 2 frames (maximal projection).

(B) Variation in pulse spacing. The plot displays the spacing (interval) between pulses for all cells in the 0.5 hr time point.

(C) The mean interval between pulses is approximately 6 min and is not subject to large developmental variation (bars reflect standard error).

(D) Developmental profile of pulse frequency (pulses per 30 min movie). Cells were scored for 1, 2, or 3+ pulses, at the indicated developmental times. There is significant variation between the proportions of the different pulse classes between 0.5 hr and 4.5 hr time points (χ2: p < 0.001).

(E) High tendency for reinitiation is observed at time points where low numbers of cells express. Ratio of the probability of a second pulse to the probability of the first (Rm) plotted against developmental time. The expected Rm value is 1 in a situation where reinitiation is not favored over de novo transcription. Cells at the 1.5 hr and 3 hr time points have a significant elevation of Rm over expected levels (χ2: p < 0.001) and are significantly different from the 4.5 hr time point (χ2: p < 0.001).