mbx2+ and rfl1+ undergo positive and negative autoregulation, respectively.
(A) Positive autoregulation of mbx2+. A strain containing N-terminal GFP-tagged mbx2+ under the control of its native promoter displayed increased GFP expression when mbx2+ was ectopically expressed with the nmt1 promoter. Nuclear GFP-Mbx2 signal and flocs in liquid culture were detected at the 9 hour induction of nmt1-driven mbx2+ in EMM minus thiamine medium. Cells were deflocculated in 2% galactose prior to fluorescence microscopy to facilitate image acquisition. The presence of galactose does not affect the GFP signal (data not shown). The bar graph compares the mean and standard deviation of cellular GFP-Mbx2 signal resulting from nmt1-driven mbx2+ and empty vector control with a significant difference of p<0.001 (Welch's two tailed t-test; n = 50, df = 52). (B) Negative autoregulation of rfl1+. A strain containing C-terminal GFP-tagged rfl1+ under native control exhibited nuclear expression (empty vector). Ectopic expression of nmt1-driven rfl1+ for 18 hours in EMM minus thiamine medium reduced the nuclear GFP signal with a slight increase in cytoplasmic GFP signal. The bar graph compares the mean and standard deviation of overall cellular Rfl1-GFP signal resulting from nmt1-driven rfl1+ and empty vector control with a significant difference of p<0.01 (Welch's two tailed t-test; n = 27, df = 44). Cells were stained with DAPI to visualize nuclei. Scale bar, 10 µm.