6DT8:
reference: Minimalism and functionality: Structural lessons from the heterodimeric N4 bacteriophage RNA polymerase II., Molodtsov V, Murakami KS, J Biol Chem. 2018 Aug 31;293(35):13616-13625. doi: 10.1074/jbc.RA118.003447. Epub, 2018 Jul 10. PMID: 29991593

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