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Cleavage factors are two closely associated
protein complex
A protein complex or multiprotein complex is a group of two or more associated polypeptide chains. Protein complexes are distinct from multienzyme complexes, in which multiple catalytic domains are found in a single polypeptide chain.
Protein c ...
es involved in the cleavage of the
3' untranslated region of a newly synthesized pre-
messenger RNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein.
mRNA is created during the p ...
(mRNA) molecule in the process of
gene transcription
Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules calle ...
. The cleavage is the first step in adding a
polyadenine tail to the pre-mRNA, which is one of the necessary
post-transcriptional modification
Transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, func ...
s necessary for producing a mature mRNA molecule.
In mammals the two cleavage factors are known as CFIm and CFIIm. The proteins that constitute these complexes are recruited to the cleavage site by
cleavage and polyadenylation specificity factor
Cleavage and polyadenylation specificity factor (CPSF) is involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA (pre-mRNA) molecule in the process of gene transcription. It is the first protein to bind to ...
and
cleavage stimulatory factor Cleavage stimulatory factor or cleavage stimulation factor (CstF or CStF) is a heterotrimeric protein, made up of the proteins CSTF1 (55 kDa), CSTF2 (64kDa) and CSTF3 (77kDa), totalling about 200 kDa. It is involved in the cleavage of the 3' sign ...
, and form a larger complex that also includes
polyadenine polymerase
In enzymology, a polynucleotide adenylyltransferase () is an enzyme that catalyzes the chemical reaction
:ATP + RNA-3'OH \rightleftharpoons pyrophosphate + RNApA-3'OH
Thus, the two substrates of this enzyme are ATP and RNA, whereas its two ...
(PAP), which performs the polyadenylation reaction.
The CFIm complex
Involved in the earliest step for the formation of the active cleavage complex, the CFIm complex is formed by three proteins of 25, 59 and 68 kDa, respectively:
*CFIm25 (or CPSF5/
NUDT21
Cleavage and polyadenylation specificity factor subunit 5 (CPSF5) is an enzyme that in humans is encoded by the ''NUDT21'' gene. It belongs to the Nudix family of hydrolases.
The protein encoded by this gene is one subunit of the cleavage factor ...
)
*CFIm59 (or
CPSF7
Cleavage and polyadenylation specificity factor subunit 7 is a protein that in humans is encoded by the ''CPSF7'' gene.
Function
CPSF7, also known as CFIm59, is the cleavage factor of two closely associated protein complexes in the 3' untransl ...
)
*CFIm68 (or
CPSF6)
CFIm25 and CFIm68 are sufficient for the activity of the complex, proving the expected redundancy of CFIm68 and CFIm59, which share great sequence similarity.
The CFIIm complex
The CFIIm complex is responsible for transcription termination and triggering the disassembly of the
elongation complex. It is composed of only two proteins:
*
PCF11
*
CLP1
References
Further reading
* Lodish H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. (2004). ''Molecular Cell Biology.'' WH Freeman: New York, NY. 5th ed.
*
{{Post transcriptional modification
Protein complexes
Gene expression