DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Common component of RNA polymerases I, II and III which synthesize ribosomal RNA precursors, mRNA precursors and many functional non-coding RNAs, and a small RNAs, such as 5S rRNA and tRNAs, respectively (By similarity). Factor that activates expression from a metal response element of the mouse metallothionein-I gene. Component of the RNA polymerase I (Pol I), RNA polymerase II (Pol II) and RNA polymerase III (Pol III) complexes consisting of at least 13, 12 and 17 subunits, respectively. Belongs to the archaeal Rpo12/eukaryotic RPC10 RNA polymerase subunit family.