Promoter activities of genes can be well-described by one or two principal components.

<p>(a) <i>fliY</i> promoter activity dynamics in 15 different measured conditions (15 combinations of conditions A,B,C,D). (b) First two principal components dynamics of <i>fliY</i>, according to principal component analysis of <i>fliY</i> dynamics in all conditions and combinations. (c) Fraction of variance explained by the first two principal components for all 94 promoters in 15 environments. Red arrows: <i>fliY</i> and rrnB with 91% and 99% explained variance. (d) <i>rrnB</i> promoter activity dynamics in 15 different measured conditions (e) The first PC of <i>rrnB</i> according to principal component analysis of <i>rrnB</i> expression dynamics in all conditions and combinations. (f) Fraction of variance explained by only the first principal components for all 94 promoters in 15 environments. Red arrows <i>fliY</i> and rrnB with 53% and 98% explained variance.