To protect themselves against chemical threats, many prokaryotes, including bacteria and archaea, employ a toxin-antitoxin (TA) system. A TA system is a set of 2 or more linked genes which together encode for both a toxin protein and a corresponding antitoxin. A TA system allows for recognition (of a toxin) and remedy (by applying the antitoxin).
There are 6 known toxin-antitoxin systems, which are classified by the physical medium the antitoxin uses to neutralize the toxin. RNA is used in types 1 and 3. The type 2 system inhibits a toxic protein by binding an antitoxin protein to it, imprisoning the toxin. Types 4–6 are less common than the first 3.
Bacteria are fond of type 2 TA. The genetic information to implement this system can be tucked into a plasmid (a tiny capsule) and shared with others – horizontal gene transfer. This helps bacterial colonies survive what would otherwise be a lethal onslaught.
A palindrome is a word that reads the same forward or backward. Civic is an exemplary palindrome.
In over 25% of known bacteria species, the instructions that tell type 2 antitoxin proteins how to do their job are encoded as palindromes. Archaea also use TA palindromes.
The especial advantage of palindromes is robustness. A portion of a palindrome may be damaged yet still be decipherable by knowing that the message is a palindrome. The coherence behind evolution can be quite the clever packager.