Kostrewa, D.D.KostrewaKuhn, C.-D.C.-D.KuhnEngel, C.C.EngelCramer, P.P.Cramer2017-09-072017-09-072015https://resolver.sub.uni-goettingen.de/purl?gro-2/1634RNA polymerase I (Pol I) is the central, 14-subunit enzyme that synthesizes the ribosomal RNA (rRNA) precursor in eukaryotic cells. The recent crystal structure of Pol I at 2.8 angstrom resolution revealed two novel elements: the 'expander' in the active-centre cleft and the 'connector' that mediates Pol I dimerization [Engel et al. (2013), Nature (London), 502, 650-655]. Here, a Pol I structure in an alternative crystal form that was solved by molecular replacement using the original atomic Pol I structure is reported. The resulting alternative structure lacks the expander but still shows an expanded active-centre cleft. The neighbouring Pol I monomers form a homodimer with a relative orientation distinct from that observed previously, establishing the connector as a hinge between Pol I monomers.enjournal_article10.1107/S1399004715012651263273740003606543000063141838