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'''RNA polymerases''', often abbreviated to '''RNAP''', are the enzymes in a cell responsible for [[transcription|synthesizing]] strands of [[RNA]].  Because this function is essential to life, all organisms (and quite a few viruses) contain at least one type of RNA polymerase.  Depending on the RNA polymerase, transcription requires either a [[DNA]] or an RNA template; although in most contexts, "RNA polymerase" refers to the DNA-dependant RNA polymerases which use a DNA template to [[transcription|transcribe]] genes into [[mRNA]] ("messenger" RNA).  [[reverse transcriptase|Reverse transcriptases]] are enzymes (usually associated with [[retrovirus|retroviruses]]) that perform the opposite function, using an RNA template to synthesize a [[DNA]] product.

'''RNA polymerases''', often abbreviated to '''RNAP''', are the enzymes in a cell responsible for [[transcription|synthesizing]] strands of [[RNA]].  Because this function is essential to life, all organisms (and quite a few viruses) contain at least one type of RNA polymerase.  Depending on the RNA polymerase, transcription requires either a [[DNA]] or an RNA template; although in most contexts, "RNA polymerase" refers to the DNA-dependant RNA polymerases which use a DNA template to [[transcription|transcribe]] genes into [[mRNA]] ("messenger" RNA).  [[Reverse transcriptase]]s are enzymes (usually associated with [[retrovirus]]es) that perform the opposite function, using an RNA template to synthesize a [[DNA]] product.

==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]]).  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.

Most [[prokaryote]]s and [[archaea]]ns use the same RNA polymerase to transcribe [[mRNA]] and functional non-coding RNAs (e.g. [[rRNA|ribosomal RNAs]] or [[tRNA|transfer RNAs]]).  Whereas [[eukaryote]]s (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 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.