Guanylyl transferases are
enzymes that transfer a
guanosine mono phosphate group, usually from
GTP to another molecule, releasing
pyrophosphate. Many
eukaryotic guanylyl transferases are
capping enzymes 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 o ...
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 p ...
. 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-ri ...
of the
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
molecule ends in a
phosphate 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. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...
residue serves as the catalytic residue 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
Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...
(tRNA) for
histidine is unique among eukaryotic tRNAs in requiring the addition of a guanine nucleotide before being
aminoacylated by the histidine
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
In enzymology, a mRNA guanylyltransferase () is an enzyme that catalyzes the chemical reaction
:GTP + (5')ppPur-mRNA \rightleftharpoons diphosphate + G(5')pppPur-mRNA
Thus, the two substrates of this enzyme are GTP and (5')ppPur-mRNA, where ...
External links
EC number 2.7.7.-- nucleotidyltransferases
References
EC 2.7.7
{{2.7-enzyme-stub