''O''
6-alkylguanine DNA alkyltransferase II (''O''
6 AGT II) previously known as ''O''
6 Guanine transferase (ogt) is an ''E. coli'' protein that is involved in
DNA repair
DNA repair is a collection of processes by which a cell (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...
together with
Ada ( also known as ''O''
6 AGT I).
Like AGT I, AGT II is responsible for the removal of
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...
groups from ''O''
6-alkyl
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 ...
, ''O''
4-alkyl
thymine
Thymine () (symbol T or Thy) is one of the four nucleotide bases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine ...
and alkyl phosphotriester in the sugar-phosphate backbone of DNA.
AGT II shows a greater preference for ''O''
4-alkyl thymine than ''O''
6-alkyl guanine and alkyl phosphotriester.
Unlike Ada, AGT II is expressed constitutively in cells.
Therefore, AGT II will repair alkylated
DNA adduct
In molecular genetics, a DNA adduct is a segment of DNA bound to a Carcinogen, cancer-causing chemical. This process could lead to the development of cancerous cells, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers ...
s even before Ada is fully induced. AGT II is similar to Ada in its
suicide inactivation in that AGT II transfers the alkyl group to a cysteine residue in its own structure, thereby inactivating itself.
The human equivalent of AGT II is ''O''
6-alkylguanine DNA alkyltransferase, a protein that in humans is encoded by the ''O''
6-methylguanine DNA methyltransferase (''MGMT'') gene. In humans, ''O''
6-alkylguanine DNA alkyltransferase preferentially removes alkyl groups from ''O''
6-alkyl guanine rather than from ''O''
6–alkyl thymine.
References
DNA repair
{{enzyme-stub