RNA polymerase

In <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an <a href="/facts/Enzyme/DSI1Fh7y">enzyme</a> that catalyzes the chemical reactions that synthesize <a href="/facts/RNA/HxPeNfNj">RNA</a> from a <a href="/facts/DNA/nB89Iauz">DNA</a> template.
Using the enzyme <a href="/facts/Helicase/IemubWzR">helicase</a>, RNAP locally opens the double-stranded DNA so that one strand of the exposed <a href="/facts/Nucleotide/pQKEwlJI">nucleotides</a> can be used as a template for the synthesis of RNA, a process called <a href="/facts/Transcription_(biology)/bDgp9HDN">transcription</a>. A <a href="/facts/Transcription_factor/wro0DPHe">transcription factor</a> and its associated transcription <a href="/facts/Mediator_complex/XxxwRobb">mediator complex</a> must be attached to a <a href="/facts/DNA_binding_site/sA6106Fj">DNA binding site</a> called a <a href="/facts/Promoter_region/YDYBzLfg">promoter region</a> before RNAP can initiate the DNA unwinding at that position. RNAP not only initiates RNA transcription, it also guides the nucleotides into position, facilitates attachment and <a href="/facts/Elongation_factor/Jas1B1cU">elongation</a>, has intrinsic proofreading and replacement capabilities, and termination recognition capability. In <a href="/facts/Eukaryote/SkwyPLMA">eukaryotes</a>, RNAP can build chains as long as 2.4 million nucleotides.
RNAP produces RNA that, functionally, is either for protein <a href="/facts/Coding_strand/o6NWI6ft">coding</a>, i.e. <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a> (mRNA); or <a href="/facts/Non-coding/zyTU8q8M">non-coding</a> (so-called "RNA genes"). Examples of four functional types of RNA genes are:

<a href="/facts/Transfer_RNA/pR9T5XSl">Transfer RNA</a> (tRNA)
Transfers specific <a href="/facts/Amino_acid/WDxYwBny">amino acids</a> to growing <a href="/facts/Polypeptide/C4ltc7UG">polypeptide</a> chains at the ribosomal site of <a href="/facts/Protein_biosynthesis/P4IcGjPd">protein synthesis</a> during <a href="/facts/Translation_(biology)/JcPC1rth">translation</a>;
<a href="/facts/Ribosomal_RNA/zy5FxddY">Ribosomal RNA</a> (rRNA)
Incorporates into ribosomes;
<a href="/facts/Micro_RNA/UjqbYYpe">Micro RNA</a> (miRNA)
Regulates gene activity; and, RNA silencing
<a href="/facts/Catalytic_RNA/yvcl3ygp">Catalytic RNA</a> (<a href="/facts/Ribozyme/yvcl3ygp">ribozyme</a>)
Functions as an enzymatically active RNA molecule.
RNA polymerase is essential to life, and is found in all living <a href="/facts/Organism/j8JkL09u">organisms</a> and many <a href="/facts/Virus/mf88Bcbl">viruses</a>. Depending on the organism, a RNA polymerase can be a <a href="/facts/Protein_complex/GW11Ee34">protein complex</a> (multi-subunit RNAP) or only consist of one subunit (single-subunit RNAP, ssRNAP), each representing an independent lineage. The former is found in <a href="/facts/Bacteria/wC8xSCsU">bacteria</a>, <a href="/facts/Archaea/Adxh0aHw">archaea</a>, and <a href="/facts/Eukaryote/SkwyPLMA">eukaryotes</a> alike, sharing a similar core structure and mechanism. The latter is found in <a href="/facts/Bacteriophage/L2Ll0T3q">phages</a> as well as eukaryotic <a href="/facts/Chloroplast/fo8U3yTx">chloroplasts</a> and <a href="/facts/Mitochondria/ErHqrdJ1">mitochondria</a>, and is related to modern <a href="/facts/DNA_polymerase/xtNLncBu">DNA polymerases</a>. Eukaryotic and archaeal RNAPs have more subunits than bacterial ones do, and are controlled differently.
Bacteria and archaea only have one RNA polymerase. Eukaryotes have multiple types of nuclear RNAP, each responsible for synthesis of a distinct subset of RNA:

<ol><li><a href="/facts/RNA_polymerase_I/ACQYJH2M">RNA polymerase I</a> synthesizes a pre-rRNA 45<a href="/facts/Svedberg/AzyatmCs">S</a> (35S in <a href="/facts/Yeast/eGD24nfI">yeast</a>), which matures and will form the major RNA sections of the ribosome.</li><li><a href="/facts/RNA_polymerase_II/MK2kgybw">RNA polymerase II</a> synthesizes precursors of mRNAs and most <a href="/facts/Small_RNA/fqhXWhb0">sRNA</a> and microRNAs.</li><li><a href="/facts/RNA_polymerase_III/PthDGwwc">RNA polymerase III</a> synthesizes tRNAs, rRNA 5S and other <a href="/facts/Small_RNA/fqhXWhb0">small RNAs</a> found in the <a href="/facts/Cell_nucleus/D7sFRa3c">nucleus</a> and <a href="/facts/Cytosol/VyXgygWm">cytosol</a>.</li><li><a href="/facts/RNA_polymerase_IV/pGk7vrlW">RNA polymerase IV</a> and <a href="/facts/RNA_polymerase_V/0F3ezKJA">V</a> found in plants are less understood; they make <a href="/facts/Small_interfering_RNA/891ytkD9">siRNA</a>. In addition to the ssRNAPs, chloroplasts also encode and use a bacteria-like RNAP.</li></ol>

RNA polymerase open-in-new

RNA polymerase