Dam (methylase)
Encyclopedia
DAM methylase
(DNA adenine methylase) is an enzyme
that adds a methyl group to the adenine
of the sequence 5'-GATC-3' in newly synthesized DNA
. Immediately after DNA synthesis
, the daughter strand remains unmethylated for a short time.
(oriC) in bacteria cells is highly controlled to ensure DNA replication occurs only once during each cell division. Part of this can be explained by the slow hydrolysis of ATP by DnaA, a protein that binds to repeats in the oriC to initiate replication. Dam methylase also plays a role because the oriC has 11 5'-GATC-3' sequences (in E. coli). Immediately after DNA replication, the oriC is hemimethylated and sequestered for a period of time. Only after this, the oriC is released and must be fully methylated by Dam methylase before DnaA binding occurs.
in uropathogenic E. coli is controlled by Dam through the methylation of the two GATC sites proximal and distal to the pap promoter.
Methylase
A methylase is an enzyme that attaches a methyl group to a molecule.These are found in prokaryotes and eukaryotes. Bacteria use methylase to differentiate between foreign genetic material and their own, thus protecting their DNA from their own immune system...
(DNA adenine methylase) is an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that adds a methyl group to the adenine
Adenine
Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
of the sequence 5'-GATC-3' in newly synthesized DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. Immediately after DNA synthesis
DNA synthesis
DNA synthesis commonly refers to:*DNA replication - DNA biosynthesis *Polymerase chain reaction - enzymatic DNA synthesis *Oligonucleotide synthesis - chemical synthesis of nucleic acids...
, the daughter strand remains unmethylated for a short time.
Role in mismatch repair of DNA
When DNA polymerase makes an error resulting in a mismatched base-pair or a small insertion or deletion during DNA synthesis, the cell will repair the DNA by a pathway called mismatch repair. However, the cell must be able to differentiate between the template strand and the newly synthesized strand. In bacteria, DNA strands are methylated by Dam methylase, and therefore, immediately after replication, the DNA will be hemimethylated. A repair enzyme, MutS, binds to mismatches in DNA and recruits MutL, which subsequently activates the endonuclease MutH. MutH binds hemimethylated GATC sites and when activated will selectively cleave the unmethylated daughter strand, allowing helicase and exonucleases to excise the nascent strand in the region surrounding the mismatch. The strand is then re-synthesized by DNA polymerase III.Role in regulation of replication
The firing of the origin of replicationOrigin of replication
The origin of replication is a particular sequence in a genome at which replication is initiated. This can either be DNA replication in living organisms such as prokaryotes and eukaryotes, or RNA replication in RNA viruses, such as double-stranded RNA viruses...
(oriC) in bacteria cells is highly controlled to ensure DNA replication occurs only once during each cell division. Part of this can be explained by the slow hydrolysis of ATP by DnaA, a protein that binds to repeats in the oriC to initiate replication. Dam methylase also plays a role because the oriC has 11 5'-GATC-3' sequences (in E. coli). Immediately after DNA replication, the oriC is hemimethylated and sequestered for a period of time. Only after this, the oriC is released and must be fully methylated by Dam methylase before DnaA binding occurs.
Role in regulation of protein expression
Dam also plays a role in the promotion and repression of RNA transcription. In E. coli downstream GATC sequences are methylated, promoting transcription. For example, Pap pilus phase variationPhase variation
Phase variation is a method for dealing with rapidly varying environments without requiring random mutation employed by various types of bacteria, including Salmonella species. It involves the variation of protein expression, frequently in an on-off fashion, within different parts of a bacterial...
in uropathogenic E. coli is controlled by Dam through the methylation of the two GATC sites proximal and distal to the pap promoter.
External links
- http://fangman-brewer.genetics.washington.edu/hemimethylation.html