Most laboratory strains of E. coli contain three site-specific DNA methylases. The Dcm methylase (encoded by the dcm gene; referred to as the Mec methylase in earlier references) methylates the internal (second) cytosine residues in the sequences CCAGG and CCTGG (1,3) at the C5 position.
What is methylation sensitivity of restriction enzymes?
Methylation-Sensitive Restriction Enzymes (MSREs) play a role in the analysis of methylated DNA, as they are used to analyze the methylation status of cytosine residues in CpG sequences. These restriction enzymes, as their name implies, are not able to cleave methylated-cytosine residues, leaving methylated DNA intact.
Are plasmids methylated?
The template plasmid, on the other hand, should be derived from a dam+ E. coli strain and will therefore have methylated adenines in any GATC sequences found in the plasmid.
How does methylation affect restriction digestion?
Many restriction enzymes are sensitive to the DNA methylation states. Cleavage may be blocked, or impaired, when a particular base in the enzyme’s recognition site is modified. Methylation sensitive restriction enzymes can be used to generate fragments for further epigenetic analysis.
What enzymes do methylation?
Protein methylation has been most studied in the histones. The transfer of methyl groups from S-adenosyl methionine to histones is catalyzed by enzymes known as histone methyltransferases. Histones that are methylated on certain residues can act epigenetically to repress or activate gene expression.
Is BamHI methylation sensitive?
Furthermore, MTases and endonucleases that recognize the same nucleotide sequence can differ in their sensitivity to non-canonical methylation. BamHI cannot methylate this modified sequence.
What factors affect restriction enzyme digestion?
The digestion activity of restriction enzymes depends on the following factors:
- Temperature: Most endonucleases digest the target DNA at 37 °C with few exceptions.
- Cofactors: Restriction endonucleases require certain cofactors or combination of cofactors to digest at the recognition site.
What happens when enzymes are blocked by dam or DCM modification?
As a result, enzymes blocked by Dam or Dcm modification will yield partial digestion patterns with λ DNA. Restriction sites that are blocked by Dam or Dcm methylation can be un-methylated by cloning your DNA into a dam –, dcm – strain of E. coli, such as dam –/dcm – Competent E. coli (NEB #C2925).
Which XbaI sites will be blocked by methylation?
For example, XbaI sites gaTˆCTAGA and TˆCTAGAtc will be blocked by methylation. To avoid dam methylation use a dam -deficient strain such as dam-/dcm – Competent E. coli ( #C2925 ).
How do you Un-methylate a restriction site?
Restriction sites that are blocked by Dam or Dcm methylation can be un-methylated by cloning your DNA into a dam–, dcm– strain of E. coli, such as dam–/dcm– Competent E. coli (NEB #C2925). Restriction sites can also be blocked if an overlapping site is present.
What is DCM methylase?
The Dcm methylase (encoded by the dcm gene; referred to as the Mec methylase in earlier references) methylates the internal (second) cytosine residues in the sequences CCAGG and CCTGG (1,3) at the C5 position.
