Diversity-generating retroelements in prokaryotic immunity

Abstract

Adaptive immunity systems found in different organisms fall into two major types. Prokaryotes possess CRISPR-Cas systems, recognizing former invaders using the memorized (captured) pieces of their DNA as the pathogen signatures. Mammals possess a vast repertory of antibodies and T-cell receptors variants generated in advance. In this second type of adaptive immunity, a pathogen presentation to the immune system specifically activates the cells expressing matching antibodies or receptors. These cells proliferate to fight the infection and to form the immune memory. The principle of preemptive production of diverse defense proteins for future use can hypothetically take place in microbes too. In this study we test the hypothesis that prokaryotes employ diversity-generating retroelements to prepare defense proteins against yet-unknown invaders. We identified several candidate defense systems and characterised them.