Figure 2.

Interactions between MCA1 and TCA1 Probed by Two-Hybrid Experiments in Yeast.

(A) Interactions between full-length MCA1 and TCA1 proteins. Interactions were assessed between the proteins indicated at the left of the figure, fused either to the AD or to the BD of the Gal4 transcription factor, by spotting serial dilutions of cotransformed yeast cells on selective medium (SD lacking Leu, Trp, and His but supplemented with 5 mM 3-AT).

(B) Interactions observed between the truncated versions of MCA1 and TCA1 schematically depicted at the left of the figure. Light-gray boxes depict the PPR repeats in the MCA1 protein, while the thick black bar indicates the shortest region of TCA1 still able to complement tca1 mutations. Growth of transformed yeast was tested as above on different selective media: –, +⁽¹⁾, and +⁽²⁾ indicate the absence of growth on any selective media, growth on medium lacking His and supplemented with 3-AT, and growth on a more stringent medium lacking His and adenine. n.t., not tested; aa, amino acids.

(C) Schematic representation of MCA1/TCA1 interactions. PPR1 and 2 represent the two blocks of PPR repeats within MCA1. The dashed arrow points to an interaction suggested, but not fully demonstrated by our experiments, between the corresponding domains.