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. 2017 Mar 20;114(14):3726–3731. doi: 10.1073/pnas.1617868114

Fig. 4.

Fig. 4.

RelQ binding to mRNA and ppGpp synthesis are mutually exclusive. (A) Although 1 mM ppGpp, ATP, or GDP alone does not affect the stability of the RelQ:mRNA(MF) complex, a combination of ATP and GDP has a strong destabilizing effect in both the presence and absence of 100 μM ppGpp. The positions of RelQ:mRNA (open red triangles) and supershifted complex in the presence of substrates (filled red triangles) are indicated to the left. (B) Increasing GDP substrate concentration in the presence of 1 mM ATP progressively destabilizes the RelQ:mRNA(MF) complex. (C) Addition of 100 μM ppGpp to RelQ both increases its catalytic efficiency (Vmax) and relaxes the positive substrate cooperativity, as shown by a decrease in the Hill constant, nH. (D) Enzymatically inactive RelQ mutant D82G (EF2671 locus numbering) forms the complex with mRNA(MF) as efficiently as the WT protein, whereas the addition of 1 mM ATP and GDP does not destabilize the complex in either the presence or absence of 100 μM ppGpp. Error bars represent SDs of the mean. Each experiment was performed at least three times.