DNA, and restriction enzymes, methylation?

Question

would like to know why these enzymes are effect less on the bacteries DNA? i mean why they couldnt cut their own DNA
23 minutes ago - 3 days left to answer.
Additional Details
11 minutes ago

thanx for answer but we have some restriction enzymes which can ignore methylation from the other organisms, i mean they can cut others dna if they are methylated. its mean that they are not always sensetive to this methylation

Answer 1

they may not have the sequence or they may have proteins bound which protect the DNA from digestion.

Answer 2

The isoschizomers MboI and Sau3AI both cleave the sequence GATC. This is the sequence that is methylated in E coli by Dam methylase on the G. The methylation blocks MboI but not Sau3AI.
List of enzymes and methylation resources
http://www.fermentas.com/techinfo/re/restrsensmeth.htm
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=309743

Dam methylation is a separate regulatory system for the bacteria not directly part of the restriction system. Not all methylation is the same.
http://openwetware.org/wiki/E._coli_restriction-modification_system