Termination factor
Encyclopedia
Termination is part of the process of transcribing RNA
. In eukaryotes, a termination factor is required to release the newly made (nascent) RNA from the transcription complex. Prokaryote
mRNAs often do not require a termination factor: an inverted repeat
followed by a string of Us (uracil
s) in the mRNA template strand forms a stem-loop structure which destabilizes binding by the RNA polymerase and causes Rho-independent transcription termination.
The most extensively studied transcriptional termination factor is the Rho protein of E. coli. The Rho protein recognizes a cytosine
-rich region of the elongating mRNA, but the exact features of the recognized sequences remain unknown. Rho forms a ring-shaped hexamer and advances along the mRNA, hydrolyzing ATP
, toward RNA polymerase
(5' to 3' with respect to the mRNA). When the Rho protein reaches the RNA polymerase
complex, transcription is terminated by dissociation of the RNA polymerase
from the DNA
. The structure, as well as the activity, of the Rho protein is similar to that of the F1 subunit of ATP synthase
, supporting the theory that the two share an evolutionary link. The antibiotic bicyclomycin works by inhibiting Rho.
The process of transcriptional termination is less well understood in eukaryotes, which have extensive post-transcriptional RNA processing. Each of the three types of eukaryotic RNA polymerase has a different termination system. Eukaryotic termination factors bind to the termination signal region and disturb RNA polymerase II
as it moves by, causing it to fall off the DNA strand within the next 300 base pairs. This 300 bp region is removed during processing, before poly(A)tailing (see Polyadenylation
).
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
. In eukaryotes, a termination factor is required to release the newly made (nascent) RNA from the transcription complex. Prokaryote
Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...
mRNAs often do not require a termination factor: an inverted repeat
Inverted repeat
An inverted repeat is a sequence of nucleotides that is the reversed complement of another sequence further downstream.For example, 5'---GACTGC....GCAGTC---3'. When no nucleotides intervene between the sequence and its downstream complement, it is called a palindrome. Inverted repeats define the...
followed by a string of Us (uracil
Uracil
Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...
s) in the mRNA template strand forms a stem-loop structure which destabilizes binding by the RNA polymerase and causes Rho-independent transcription termination.
The most extensively studied transcriptional termination factor is the Rho protein of E. coli. The Rho protein recognizes a cytosine
Cytosine
Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
-rich region of the elongating mRNA, but the exact features of the recognized sequences remain unknown. Rho forms a ring-shaped hexamer and advances along the mRNA, hydrolyzing ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, toward RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
(5' to 3' with respect to the mRNA). When the Rho protein reaches the RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
complex, transcription is terminated by dissociation of the RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
from the DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. The structure, as well as the activity, of the Rho protein is similar to that of the F1 subunit of ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
, supporting the theory that the two share an evolutionary link. The antibiotic bicyclomycin works by inhibiting Rho.
The process of transcriptional termination is less well understood in eukaryotes, which have extensive post-transcriptional RNA processing. Each of the three types of eukaryotic RNA polymerase has a different termination system. Eukaryotic termination factors bind to the termination signal region and disturb RNA polymerase II
RNA polymerase II
RNA polymerase II is an enzyme found in eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase...
as it moves by, causing it to fall off the DNA strand within the next 300 base pairs. This 300 bp region is removed during processing, before poly(A)tailing (see Polyadenylation
Polyadenylation
Polyadenylation is the addition of a poly tail to an RNA molecule. The poly tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature messenger RNA for translation...
).