Growing evidence suggests that transcriptional regulatory networks in many organisms are highly flexible. More precisely, the comparison of the transcriptional regulatory networks of ascomycetes suggests that both cis- and trans-regulatory elements involved in the control of metabolic pathways have dramatically changed between species. By using the latest technologies of Chromatin immunoprecipitation coupled with tilling DNA microarrays (ChIP-chip) and bioinformatic analysis of multiple-species genomes, we seek to reconstruct the evolutionary path that lead to the rearrangements of the transcriptional regulatory networks.

In recent years we and others have shown that dramatic rearrangements of the transcriptional regulatory components of metabolic functions have occurred among ascomycete species ^[1]. In particular, recent work has shown that transcriptional rewiring is common in regulons controlling processes such as production of ribosome components and metabolism of carbohydrates and lipids ^[2].

Conserved metabolic machineries direct energy production and investment in most life forms. However, variation in the transcriptional regulation of the genes that encode this machinery has been observed and shown to contribute to phenotypic differences between species. Here ^[2], we show that the regulatory circuits governing the expression of central metabolic components (in this case the ribosomes) in different yeast species have an unexpected level of evolutionary plasticity. Most transcription factors involved in the regulation of expression of ribosomal genes have in fact been reused in new ways during the evolutionary time separating S. cerevisiae and C. albicans to generate global changes in transcriptional network structures and new ribosomal regulatory complexes.