![]() RNA polymerase III (Pol III) transcribes small non-coding RNAs, including tRNAs, 5S rRNA, U6 snRNA, SRP RNA, and other stable short RNAs such as ribonuclease P RNA. For example, precursor mRNAs (pre-mRNAs) are extensively processed before exiting into the cytoplasm through the nuclear pore for protein translation. Many Pol II transcripts exist transiently as single strand precursor RNAs (pre-RNAs) that are further processed to generate mature RNAs. RNA polymerase II (Pol II) is responsible for the transcription of all mRNAs, some snRNAs, siRNAs, and all miRNAs. The transcription of rRNA genes takes place in a specialised structure of the nucleus called the nucleolus, where the transcribed rRNAs are combined with proteins to form ribosomes. ![]() This precursor is then processed into three rRNAs: 18S, 5.8S, and 28S. These rRNA genes are organised into a single transcriptional unit and are transcribed into a continuous transcript. RNA polymerase I (Pol I) catalyses the transcription of all rRNA genes except 5S. Transfer RNA ( tRNA), other small RNAs (including the small 5S ribosomal RNA (5s rRNA), snRNA U6, signal recognition particle RNA (SRP RNA) and other stable short RNAs Nucleus (and possibly the nucleolus- nucleoplasm interface) Messenger RNA ( mRNA), most small nuclear RNAs ( snRNAs), small interfering RNA ( siRNAs) and microRNA ( miRNA). Larger ribosomal RNA ( rRNA) ( 28S, 18S, 5.8S) Main article: RNA polymerase § EukaryotesĮukaryotes have three nuclear RNA polymerases, each with distinct roles and properties. These non-coding RNAs perform a variety of important cellular functions. More abundantly made are the so-called non-coding RNAs account for the large majority of the transcriptional output of a cell. Protein coding genes are transcribed by RNA polymerase II into messenger RNAs (mRNAs) that carry the information from DNA to the site of protein synthesis. For example, structural components of the ribosome are transcribed by RNA polymerase I. The RNAs transcribed serve diverse functions. ![]() The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.Įukaryotic transcription proceeds in three sequential stages: initiation, elongation, and termination. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Unlike prokaryotic RNA polymerase that initiates the transcription of all different types of RNA, RNA polymerase in eukaryotes (including humans) comes in three variations, each translating a different type of gene. Gene transcription occurs in both eukaryotic and prokaryotic cells. Eukaryotic transcription is the elaborate process that eukaryotic cells use to copy genetic information stored in DNA into units of transportable complementary RNA replica.
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