Figure legend : The superimposition procedure was performed for the 3D-gene expression networks shown in Figure 2, with w = 2. Only S. cerevisiae genes were moved. (A) Biplot representing each S. cerevisiae gene according to its final Ei (X-axis) and Deltai (Y-axis) values (see Methods). In cases of multiple links, the average Ei value was calculated. Genes contained in each temporal classes are shown in different colours on the plot (blue = "Nitrogen", green = "Early", red = "Middle", yellow = "Late"). (B) Expression profiles of four S. cerevisiae genes (ATG8, DAL5, AZR1 and ADY2), underlined on the biplot shown in (A). The expression profiles of their orthologous genes in S. pombe are also represented to allow direct visual comparison, with the correlation measure between the expression values that are common to the S. pombe and S. cerevisiae time series in square brackets. As expected, the orthologous pairs 1 and 2 show very similar expression profiles between S. cerevisiae and S. pombe, whereas pairs 4 and 5 show dissimilar expression profiles. The case of the orthologous gene pair number 3 (YHR087W and SPBC21C3.19) deserves a special mention. Even if the expression profiles are not strickly identical (the correlation value is only 0.36), the correponding final Ei and Deltai values are low. Indeed, these orthologous genes are both induced at the end of the time course and thus occupy a similar external position in the S. pombe and S. cerevisiae gene expression networks (see Figure 2, horizontal arrow).