6FGK:
reference: Structural and mechanistic divergence of the small (p)ppGpp synthetases RelP and RelQ., Steinchen W, Vogt MS, Altegoer F, Giammarinaro PI, Horvatek P, Wolz C, Bange G, Sci Rep. 2018 Feb 1;8(1):2195. doi: 10.1038/s41598-018-20634-4. PMID: 29391580

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