InterPro domain: IPR015699

DNA-dependent RNA polymerases ( 2.7.7.6 ) are responsible for the polymerisation of ribonucleotides into a sequence complementary to the template DNA. In eukaryotes, there are three different forms of DNA-dependent RNA polymerases transcribing different sets of genes. Most RNA polymerases are multimeric enzymes and are composed of a variable number of subunits. RNA synthesis follows after the attachment of RNA polymerase to a specific site, the promoter, on the template DNA strand. The RNA synthesis process continues until a termination sequence is reached. The RNA product, which is synthesised in the 5' to 3' direction, is known as the primary transcript.

Eukaryotic nuclei contain three distinct types of RNA polymerases that differ in the RNA they synthesise:

1. RNA polymerase I: located in the nucleoli, synthesises precursors of most ribosomal RNAs.

2. RNA polymerase II: occurs in the nucleoplasm, synthesises mRNA precursors.

3. RNA polymerase III: also occurs in the nucleoplasm, synthesises the precursors of 5S ribosomal RNA, the tRNAs, and a variety of other small nuclear and cytosolic RNAs.

Eukaryotic cells are also known to contain separate mitochondrial and chloroplast RNA polymerases. Eukaryotic RNA polymerases, whose molecular masses vary in size from 500 to 700kDa, contain two non-identical large (greater than 100kDa) subunits and an array of up to 12 different small (less than 50kDa) subunits.

This entry represent the largest subunit of DNA-directed RNA polymerase I, which constitutes the catalytic core component of RNA Pol I [ 1 ].

1. RNA polymerase I structure and transcription regulation. Nature 502, 650-5