Figure 1

The gene regulatory network from [21], its mRNA interactions and the corresponding diagram for the network modified by [17]. (a) The gene regulatory network from [21]. Rectangles denote promoters, zigzags indicate mRNAs and circles stand for proteins, dimers and a ligand (Q). The symbols + and - indicate whether transcription of a gene is activated or inhibited by relevant transcription factor. The subnetwork involving the genes A and B is a hysteretic oscillator [22]. Protein A activates transcription of both genes. Protein B joins it forming a dimer AB, which reduces the amount of free protein A and, consequently, inhibits transcription. Thus oscillations appear. The genes C and D compose a switch [23]: each protein forms a dimer which acts as an inhibitor of transcription of the other gene. Therefore highly expressed gene switches off expression of the other. The ligand binding mechanism [24] is represented by the subnetwork involving the genes E and F: protein E joined with a ligand Q forms an activator of transcription of the gene F. Finally, there are two cascades: in the first cascade C inhibits G and G inhibits H, while in the second cascade C inhibits K and K activates J. (b) The mRNA interactions in the above network; solid arrows denote transcriptional regulation, dashed ones represent interactions triggered by the ligand and posttransciptional regulation, (c) The corresponding diagram for the network modified by [17].