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==Types==
==Types==
Most [[prokaryote|prokaryotes]] and [[archaea|archaeans]] use the same RNA polymerase to transcribe [[mRNA]] and functional non-coding RNAs (e.g. [[rRNA|ribosomal RNAs]] or [[tRNA|transfer RNAs]]. However, [[eukaryote|eukaryotes]] (organisms in which the genetic material is contained within a [[nucleus]]) use specialized RNAPs, each responsible for transcribing different classes of RNA.
Most [[prokaryote|prokaryotes]] and [[archaea|archaeans]] use the same RNA polymerase to transcribe [[mRNA]] and functional non-coding RNAs (e.g. [[rRNA|ribosomal RNAs]] or [[tRNA|transfer RNAs]]). Whereas [[eukaryote|eukaryotes]] (organisms in which the genetic material is contained within a [[nucleus]]) use specialized RNAPs, each responsible for transcribing different classes of RNA.
RNA polymerase II (abbreviated RNAP II or RNA Pol II), is the enzyme responsible for transcribing the vast majority of protein-coding genes in eukaryotes. It is also responsible for transcribing the majority of genes encoding [[snRNA|short nuclear RNAs]] (snRNAs) and [[miRNA|micro RNAs]] (miRNAs). As such, RNAP II is the most well-studied and well understood of the eukaryotic RNAPs. Genes transcribed by RNAP II are referred to as "type II genes" and comprise the vast majority of genes present in eukaryotic genomes.
RNA polymerase I (RNAP I or RNA Pol I) transcribes most of the [[rRNA|ribosomal RNAs]] in a eukaryotic cell. RNA polymerase III (RNAP III or RNA pol III) transcribes the [[transfer RNA|tRNA]] precursors, as well as the 5S rRNA, the U6 snRNA (involved in [[RNA processing|RNA splicing]])and various other small functional RNA products.