Casposons of Bacteria and Archaea: survey, characterization and evolutive aspects

Abstract

Mobile genetic elements (MGE) are biological entities that are able to insert their genetic content into the chromosome of a host cell. The importance of MGEs in the biology of prokaryotes and eukaryotes has been increasingly recognized, both in basic and in applied research. Recently, a new group of elements, named casposons, was discovered. The elucidation of the ancestral position of its endonuclease Cas1 in the phylogeny of this family of proteins suggests that these elements played a fundamental role in the development of the adaptive immunity of prokaryotes and in the origin of CRISPRs . Our group has recently developed two bioinformatics tools: TABAJARA - for the rational design and construction of profile HMMs, and e-Finder, for the application of these models in the detection of multigene elements from assembled genomes. With the use of these programs, we succeed to perform a large-scale survey of casposons from bacterial archaeal genomes in a previous project. The present project aims to extend this survey and characterization in regard to the structure, functions and evolutionary relationships of casposons. A possible evolutionary relationship between casposons and phages associated to the Tectiviridae family was recently discovered, characterized by elements presenting gene of a capsid protein containing a double-jelly roll domain. We intend to specifically search for elements containing Cas1 and PolB genes, together with capsid proteins, aiming at identifying possible missing links in the evolution of these elements. Our group already has a collaboration with Dr. Mart Krupovic, the discoverer of casposons and the world's greatest authority on the subject, and the preliminary work has demonstrated the viability of our proposal. A broader knowledge of the diversity of casposons may reveal new important aspects in the evolution of these elements, their relationship with phages and their role in the origin of CRISPRs and in the development of adaptive immunity of prokaryotes.