Fig. 1.

Stochastic expression of HOpr in WT (wt) and swi5 cells. (A) Movie clips of the growth of the wt cells (HOpr-GFP MYO1-mCherry). Daughter cycle (the first cell cycle after birth) and mother cycle (the subsequent cell cycles after separating with the first bud) can be clearly differentiated in the movie. The intensity of the GFP reflects the activity of the HOpr, and the red dot is the Myo1-mCherry. Three cells were tracked with different colored arrows. The white-labeled cell went through multiple mother cycles with GFP expressed once every cell cycle; the blue-labeled cell has one daughter cycle (no expression), followed by two mother cycles (strong expression). Both cells follow the “typical” GFP expression pattern. In contrast, the pink-labeled cell represents a rare case in which GFP is turned on during the daughter cycle. d, daughter cycle; m, mother cycle. (B) GFP intensity vs. time traces driven by HOpr in a single wt cell. The dashed vertical lines represent the cell division times measured by the disappearance of the Myo1 ring. (C) Histogram of the amplitude of GFP expression in wt mother and daughter cycles. The expression amplitudes are calculated as the peak-to-trough difference in the GFP signal during a given cell cycle, and they are normalized so that the average expression level in mother cycles is 1. Note the discontinuity in the y axis. (D–F) Same as in A–C, except in the swi5 strain (DY14800). In this case, HOpr is repressed in most of the cell cycles (e.g., the white-labeled cell in D). However, there are rare cells with sporadic HO expression in both mother and daughter cycles (e.g., the blue- and pink-labeled cells in D). Example traces of GFP intensity (E) and a histogram of GFP expression amplitude (F) are shown.