Escherichia coli/Methylation


 * Type I methylation systems:
 * E. coli K-12 restricts DNA which is not protected by adenine methylation at sites AA*C[N6]GTGC or GCA*C[N6]GTT, encoded by the hsdRMS genes(EcoKI).  Deletions in these genes removes either the restriction or methylation or both of these functions.
 * E. coli B derivative strains contain an hsdRMS system (EcoBI) restricting and protectiing the sequence TGA*[N8]TGCT or AGCA*[N8]TCA.
 * The mcrA gene (carried on the e14 prophage) restricts DNA which is methylated in CmCWGG or mCG sequences (methylation by the dcm gene product).
 * The mcrBC genes restrict RmC sequences.
 * The mrr gene product restricts adenine methylated sequences at CAG or GAC sites.
 * E. coli methylates the adenine in GATC (and the corresponding A on the opposite strand) with the dam gene product.
 * M.EcoKII methylates the first A at the palindromic site ATGCAT (as well as the corresponding A on the opposite strand), see (Kossykh VG (2004) J. Bact 186: 2061-2067 PMID 15028690)  Note that this article has been retracted; the retraction appears to center on textual plagarism, not experimental results.  The homology to AvaIII is real.  I think I believe it. tk 20:28, 9 December 2005 (EST).  Rich Roberts reports: "We have tried ourselves to detect activity with this gene product and cannot detect any methyltransferase activity.  In our case we used antibodies able  to detect N6-methyladenine or N4 methylcytosine in DNA.  The ones we have are very sensitive and should have been able to detect 5 methyl groups in the whole E. coli chromosome.  Nothing was detected in an over expressing strain."
 * For additional information see E. coli restriction-modification system and the NEB technical information on methylation.