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What does RNA polymerase do?

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The Takeaway: RNA polymerase is a critical tool used to convert the information in DNA to RNA, which is the entire basis of gene expression research. Read on to learn how fast it can create mRNA. 

To say that RNA polymerase is important is an understatement. This abundant enzyme is THE molecular tool to use if you want to transcribe DNA to RNA. RNA polymerase, or RNAP, does more than copy DNA—it also screens nucleotides to ensure they are complementary to the gene, it recognizes DNA sequences so it attaches to the correct location, it proofreads its work, it responds to its associated transcription factors, and it terminates at the correct location, too.

Are you looking for an RNA polymerase definition? Not totally familiar with RNA polymerase and want to learn more? Here you go!

What does RNA polymerase do?

RNA polymerase is an enzyme that copies a DNA sequence in to an RNA sequence during transcription. Transcription is the first step in gene expression, and leads to translation, the process in which RNA is decoded into protein.

When was RNA polymerase discovered?

RNA polymerase was discovered by American biochemist Arthur Kornberg and Spanish biochemist and physician Severo Ochoa in 1956. The pair won the Nobel Prize in Physiology or Medicine in 1959. The pair was working at Washington University in St. Lous, investigating enzyme purification techniques, and in 1956 isolated what today is known as DNA polymerase I. Kornberg went on to study spores and the metabolism of inorganic polyphosphate, while Ochoa continued research on protein synthesis and the replication of RNA viruses; both men remained active in research and academia for decades after their big discovery.

What is DNA polymerase?

DNA polymerase is separate from RNA polymerase. A DNA polymerase is an enzyme that synthesizes DNA during replication. Both RNA and DNA polymerases are critical in DNA replication and usually work in a complex to create two identical DNA duplexes.

What is RNAP?

RNAP is short for RNA polymerase.

Is RNA polymerase used in translation?

No, RNA polymerase is not used in translation. It is used in transcription. Transcription refers to the synthesis of RNA from a DNA template, while translation is the process of converting messenger RNA into protein.

What is bacterial RNA polymerase?

Bacterial RNA polymerase is responsible for transcription in bacteria. Bacterial RNAP recognizes promoter DNA and begins transcription.

RNA polymerase structure and function

RNA polymerase enzymes contain several subunits, while the prokaryotic RNA polymerase form has four subunits that are in charge of transcription. Eukaryotes have at least eight subunits and they are tasked with attaching and processing DNA through transcription.

There are three to four stages of transcription that involve RNA polymerase—depending on the organism:

Initiation: Initiation begins when RNA polymerase binds to the DNA at the designated promoter region with the help of enzymes that remodel the chromatin structure (in eukaryotes) and enzymes that open the double-stranded DNA.

Promoter proximal pausing (mammals and metazoans): Like the pit crew preparing the car for a race, RNA polymerase II is surrounded by a variety of supporting transcription factors. The entire complex pauses just downstream from the transcription start site, which mediates the rate of transcription, but the jury is still out as to the full function of the paused complex.

Elongation: Elongation begins as the RNA polymerase complex unwinds the double-stranded DNA into two single strands, in which the template strand become the code for RNA synthesis. Two key factors dominate this stage:

  • Processivity of RNA polymerase is essential for making it to the end of the gene.
  • Elongation rate is the number of nucleotides synthesized per unit of time. 

Termination: Termination is the last step in the transcription process. When RNA polymerase runs into a terminator sequence or terminator signal, it slows down its speed of adding to the RNA strand, the RNA transcript is released, and the transcript for that DNA template ends. Two mechanisms may be involved with the release:

  • Slowing down causes the pit crew of transcription factors to fall off, which changes the interaction between RNA polymerase and DNA.
  • Slowing down of RNA polymerase around the polyA tail addition site allows the “torpedo” endonuclease, XRN1, to swoop into the race and degrade the RNA that is made after passing the polyA site (PAS).

Three kinds of RNA polymerases

There are three types of RNA polymerases: RNA polymerase I, RNA polymerase II, and RNA polymerase III. These are often abbreviated as RNA poly I, RNA poly II, and RNA poly III. Each of them has special roles:

  • Polymerase I synthesizes the three largest ribosomal RNAs, which synthesize proteins from messenger RNA.
  • Polymerase II transcribes protein-encoding genes and non-coding RNA.
  • Polymerase III synthesizes transfer RNA and 5s rRNA.

The speed of RNA polymerase II transcription

RNA polymerase is found in all living creatures, and even nonliving things like viruses. There have been numerous studies to see how fast RNA polymerase can transcribe, and the range of these speeds is quite large. Since slowing down is essential to transcription termination, speed of transcription is regulated, and biochemical studies clocked it between 1100 bases/min and 4800 bases/min. Quantitative methods clocked RNA polymerase between 3100 bases/min and 3800 bases/min. But these were based on only a few genes.

Using next generation sequencing, researchers studied RNA polymerase on a global, well, genome-wide scale, to find out the speed varied from 1250 bases/min to 3500 bases/min. Interestingly, the speed depends on the gene—some are transcribed faster than others. Its speed varies from slow at the beginning, increases in the middle regions, and then slows at the termination signals. RNA polymerase is faster when it is activated by certain conditions, but other conditions result in slower transcription. So, it turns out that RNA polymerase speed of transcription provides yet another fundamental way our cells, tissues, and ultimately our whole being control gene expression in response to the environment.

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