Figure 2

Automatic reasoning. Illustrating the consistency criteria. A. Signed and oriented regulatory network, arrows ending with '- >' or '-|' represent activations or inhibitions respectively. B. Detection of a global inconsistency when rpsP and rpmC are both observed to be down-regulated. Step 1, rpsP's negative change implies that its only inhibitor has to be up-regulated (fnr = +); Step 2, fnr's positive change implies that its only inhibitor has to be down-regulated (arcA = -); Step 3, these deductions cannot explain rpmC's down-regulation, since its activator (fnr) is up-regulated and its inhibitor (arcA) is down-regulated. C. Prediction when rpsP is observed to be up-regulated and rpmC, down-regulated. rpsP's inhibitor (fnr) is fixed to '-' to explain the observed value of rpsP, in a similar manner, arcA is fixed to '+'; with this unique configuration we obtain a consistent system where fnr = - and arcA = + are the predictions.