Analysis of interaction between Arabidopsis GGPS isoforms with PSY. Yeast strains expressing Nub (N) or N-terminal Nub fusions with Arabidopsis GGPS isoforms 2, 6, 8, 9, 10, and 11 were combined with yeast strains expressing Cub only (C) or C-terminal Cub fusion with Arabidopsis PSY, respectively. Corresponding Nub/Cub fusions with the Arabidopsis kation channel protein KAT1 were used as negative controls whereas dimerization of Nub-KAT1/KAT1-Cub served as a positive control. A, Interaction assay. Growth on selective medium, supplemented with 150 µM Met after 2 d incubation. B, β-Gal activity determined by ONPG assays of yeast strains coexpressing combinations with PSY-Cub. C, Nub-GGPS protein levels in PSY-Cub combinations. Nub-GGPS proteins carried an N-terminal 3-HA tag and were detected using a 3-HA antibody. D, Phytoene amounts in PSY-Cub combinations, quantified by HPLC. E, Absorption spectrum of phytoene determined in yeast strains coexpressing PSY-Cub and GGPS11. Results in B and D are mean +/− SEM of three biological replicates. * Significant difference to that in Nub control (P > 0.05).