Figure 4.

Inhibition of Dimer Formation of CCA1α and LHY by CCA1β.

(A) Expression constructs used in yeast three-hybrid assays. The CCA1β cDNA was expressed under control of the Met-suppressible promoter (pMET25-CCA1β). Gray boxes represent sequence regions containing MYB domains.

(B) and (C) Inhibition of CCA1α dimer formation by CCA1β in yeast cells. Yeast three-hybrid assays were performed, and cell growth on selective media (-LWHM) (B) and β-Gal activities (C) were examined. Note that the CCA1β gene is not expressed on selective media without Leu, Trp, and His (-LWH) but is expressed on selective media without Leu, Trp, His, and Met (-LWHM). In (C), β-Gal activities were measured in the presence or absence of Met. Five measurements were averaged, and statistical significance of the measurements was determined using a Student’s t test by comparing the β-Gal activity in the presence of Met (*P < 0.01). Bars indicate the se.

(D) Inhibition of CCA1α-CCA1α, LHY-LHY, and CCA1α-LHY dimer formations by CCA1β in Arabidopsis protoplasts. The BiFC assays were performed as described in Figure 2E. Each photograph is a representative of protoplasts (n > 30) that exhibit similar patterns of fluorescence signals. White arrows indicate YFP fluorescence.