Restriction Enzyme Warfare...???? I just had an idea, and I wonder if it has ever been found in bacteria at all. Bacteria have restriction enzymes which cut specific recognition sites in DNA (Click here if you want to find out more about Restricton enzymes:Restriction Enzyme Tutorial ). It is theorised that these evolved as a protective measure against Viruses. Restriction enzymes exist in bacteria, floating around as they do, and so of course, the bacterial DNA couldn't have any segment in it which has that particular sequence (If that sequence existed in the bacteria, then the restriction enzyme would cut that site, and the bacteria would quickly cease to exist). Now, I know that many bacteria out there use various mechanism to destroy organisms around them as a way of getting rid of competition, and allowing them free reign over any nutrients present (Penecillin comes from a mould... The mould produces penecillin to kill bacteria around it, so it can eat all the food (and probably them too as they fall apart)) (I think). Now, here is the thought: I wonder if any bacteria has ever implemented Restriction Enzymes as a method of killing bacteria around it to destroy competition from foreign species. Its probably too complicated an operation for it to evolve, considering that the same end can be achieved with other mechanisms (like the penecillin example), but it just occured to me that if it did occur, then at least it would be species specific. It could either occur by some sort of Pilus analogous mechanism (either injecting a plasmid coding the ....Oh no, injecting DNA would never work, because different species wouldn't respond to the same promoters. So it would need to inject the protein directly into the bacteria...which is probably quite difficult. Hmm, i probably shouldn't post this now, but since I have typed it all out... i don't want to waste it all.