In molecular biology, the PyrG leader is a
''cis''-regulatory RNA element found at the
5' of the PyrG
mRNA
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 Protein biosynthesis, synthesizing a protein.
mRNA is ...
. The PyrG gene encodes a
CTP synthase
CTP synthase is an enzyme () involved in pyrimidine biosynthesis that interconverts UTP and CTP.
Reaction mechanism
CTP (cytidine triphosphate) synthetase catalyzes the last committed step in pyrimidine nucleotide biosynthesis:
ATP + UTP + ...
, which is involved in
pyrimidine biosynthesis
Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other ...
. The PyrG leader
regulates expression of PyrG, PyrG can form into two different
hairpin structures, a terminator or an anti-terminator. Under low
CTP conditions,
guanine
Guanine () (symbol G or Gua) is one of the four main nucleotide bases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine ( uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside ...
(G) residues are incorporated at a specific site within the PyrG leader, these allow
base-pairing
A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
with a
uracil
Uracil () (nucleoside#List of nucleosides and corresponding nucleobases, symbol U or Ura) is one of the four nucleotide bases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via ...
(U)-rich region and the formation of an anti-terminator loop, this results in increased expression of PyrG. Under high CTP conditions the guanines are not added, the anti-terminator loop cannot form and instead a terminator loop is formed, preventing further PyrG expression.
Further reading
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References
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Cis-regulatory RNA elements