Guanylyl transferases are
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
s that transfer a
guanosine mono phosphate group, usually from
GTP to another molecule, releasing
pyrophosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates a ...
. Many
eukaryotic
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
guanylyl transferases are
capping enzyme
A capping enzyme (CE) is an enzyme that catalyzes the attachment of the 5' cap to messenger RNA molecules that are in the process of being synthesized in the cell nucleus during the first stages of gene expression. The addition of the cap occurs ...
s that catalyze the formation of the
5' cap
In molecular biology, the five-prime cap (5′ cap) is a specially altered nucleotide on the 5′ end of some primary transcripts such as precursor messenger RNA. This process, known as mRNA capping, is highly regulated and vital in the creation ...
in the
co-transcriptional modification of
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 ...
. Because the
5' end
Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar-r ...
of the
RNA
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
molecule ends in a
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
group, the bond formed between the RNA and the GTP molecule is an unusual 5'-5' triphosphate linkage, instead of the
3'-5' linkages between the other nucleotides that form an RNA strand. In capping enzymes, a highly conserved
lysine
Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...
residue serves as the
catalytic residue
In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the ''binding si ...
that forms a covalent enzyme-GMP complex.
[Fresco LD, Buratowski S. (1994). Active site of the mRNA-capping enzyme guanylyltransferase from Saccharomyces cerevisiae: similarity to the nucleotidyl attachment motif of DNA and RNA ligases. ''Proc Natl Acad Sci USA'' 91(14): 6624–6628.]
The transfer RNA (tRNA) for histidine is unique among eukaryotic tRNAs in requiring the addition of a guanine nucleotide before being aminoacylation, aminoacylated by the histidine aminoacyl tRNA synthetase, tRNA synthetase. The yeast guanylyl transferase specific to tRNA
His is unique in being the only known non-tRNA synthetase enzyme that specifically recognizes the tRNA anticodon.
[Jackman JE, Phizicky EM. (2006). tRNAHis guanylyltransferase adds G–1 to the 5' end of tRNAHis by recognition of the anticodon, one of several features unexpectedly shared with tRNA synthetases. ''RNA'' 12:1007-1014.]
Guanylyl transferases also exist for transferring guanosine nucleotides to sugar molecules, such as mannose and fucose.
See also
* mRNA guanylyltransferase
References
External links
EC number 2.7.7.-- nucleotidyltransferases
EC 2.7.7
{{2.7-enzyme-stub