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. 2015 Mar 27;11(3):e1004129. doi: 10.1371/journal.pcbi.1004129

Fig 1. Main components and interactions involved in the reaction to combined nitrogen deprivation in cyanobacteria.

Fig 1

Rectangular boxes represent genes (ntcA, hetR and patS) while rounded boxes and circles represent transcription factors (NtcA, HetR and PatS) and smaller molecules (2-OG and cN) respectively. Normal-tipped and flat-tipped arrows stand for up-regulating and down-regulating processes respectively. Dashed lines stand for indirect or imperfectly understood interactions. The accumulation of 2-OG enhances the DNA-binding activity of NtcA, which in turn up-regulates the transcription of ntcA and hetR. HetR activates ntcA and hetR (composing the central NtcA-HetR autoregulatory loop), the inhibitor patS and other genes that lead to nitrogen fixation and the morphological changes involved in heterocyst differentiation. 2-OG and cN levels are linked through the GS/GOGAT cycle (see Fig. 2).