A composite feed-forward loop I4-FFL involving IHF and Crc stabilizes expression of the XylR regulator of Pseudomonas putidamt-2 from growth phase perturbations
Abstract
Genetic networks are typically composed of a series of connected motifs that confer specific logic and dynamic properties to the resulting circuits. While some feed forward loop (FFL) variants abound in such networks, others (e.g. the type-4 incoherent FFL or I4-FFL) are virtually absent from the known regulatory devices. We report here that the key node that rules the expression of the m-xylene biodegradation pathway of the soil bacterium Pseudomonas putidamt-2 merges opposite physiological effects of the growth phase by means of a regulatory device based on the rarely found I4-FFL motif. Specifically, the FFL includes the integration host factor (IHF), which both co-activates the master Pu promoter and represses transcription of its cognate regulatory gene xylR at the onset of the stationary phase. On the other hand, the catabolite repression control (Crc)