Dam methylation - XbaI (Nov/12/2005 )

XbaI is an enzyme sensitive to Dam methylation, it is blocked by overlaping.

Phage 434 in this bioforum explained me what this type of methylation means:
«Overlapping methylation here refers to the common DAM methylation in most lab strains of E. coli, which methylates the A in GATC sequences. Since the XbaI site is TCTAGA, if it is followed by a TC sequence, then the XbaI site will be tctaGATC. The A of the GATC site will be 6-methylated by DAM, and the XbaI restriction enzyme will be blocked. The overlap (of course) could be on the other end of the XbaI site -- such as GATCtaga. This will methylate the A on the opposite strand of the "T" in GATC»

But I still don´t understand why this site is methylated as there is no GA before XbaI site nor TC after it. Where is the GATC sequence recognized by the methylase????

The sequence where is the XbaI site is the following:
5´CATCTAGAGC 3´

If we think in the DNA sequence in terms of double stranded...then the sequence is the following:
5´CATCTAGAGC 3´
3´GTAGATCTCG 5´

Can methylase recognize sequence GATC within the XbaI site? Is the following sequence (in bold) the one that is recognized by the Dam methylase?
3´GTAGATCTCG 5´


Thanks

no because dam recognises GATC read from 5'-3'

what you have in bold is CTAG (read 5' tp 3'), i don't think dam methylase will methylate this.

a good site to goto is
http://rebase.neb.com/cgi-bin/damlist?eXbaI

and this tells you the methylatopn sensitivity of XbaI

good luck

Nick

I cannot open this link!

Is it correct?

oops sorry !!!

try and goto here:


http://rebase.neb.com/

and look up XbaI

Nick