?|cl19114: RNAP_largest_subunit_N Superfamily
Largest subunit of RNA polymerase (RNAP), N-terminal domainThis region represents the N-terminal domain of the largest subunit of RNA polymerase (RNAP). RNAP is a large multi-protein complex responsible for the synthesis of RNA. It is the principle enzyme of the transcription process, and is a final target in many regulatory pathways that control gene expression in all living cells. At least three distinct RNAP complexes are found in eukaryotic nuclei; RNAP I transcribes the ribosomal RNA precursor, RNAP II the mRNA precursor, and RNAP III the 5S and tRNA genes. A single distinct RNAP complex is found in prokaryotes and archaea, respectively, which may be responsible for the synthesis of all RNAs. Structure studies reveal that prokaryotic and eukaryotic RNAPs share a conserved crab-claw-shaped structure. The largest and the second largest subunits each make up one clamp, one jaw, and part of the cleft. All RNAPs are metalloenzymes. At least one Mg2+ ion is bound in the catalytic center. In addition, all cellular RNAPs contain several tightly bound zinc ions to different subunits that vary between RNAPs from prokaryotic to eukaryotic lineages. This domain represents the N-terminal region of the largest subunit of RNAP, and includes part of the active site. In archaea and some of the photosynthetic organisms or cellular organelle, however, this domain exists as a separate subunit.