Heat map of the expression of ABC transporter genes in Tetrahymena. The levels of expression are illustrated by different grades of color as determined from microarray data indicated along the top (From left to right). The color scale is as follows: dark color, low expression; light color, high expression. Levels of expression were obtained for 20 points in time during three physiological/development stages of the life cycle of Tetrahymena: For growing cells, L-l, L-m and L-h correspond to ~1×105 cells/ml, ~3.5×105 cells/ml and ~1×106 cells/ml, respectively. For measurements of expression during starvation, ~2×105 cells/ml were collected at intervals of 0, 3, 6, 9, 12, 15 and 24 hours (referred to as S-0, S-3, S-6, S-9, S-12, S-15 and S-24, respectively). For measurements of expression during conjugation, equal volumes of B2086 and CU428 cells were mixed together in culture, and samples were collected at intervals of 0, 2, 4, 6, 8, 10, 12, 14, 16 and 18 hours after mixing (referred to as C-0, C-2, C-4, C-6, C-8, C-10, C-12, C-14, C-16 and C-18, respectively). The following three categories could be identified: a, silent genes or those with low expression levels (some points may silent); b, genes highly expressed only for specific conditions; c, genes with continuous high expression levels.