Krupovic, M. et. al. (2017) Current Opinion in Microbiology 38:36-43. https://www.ncbi.nlm.nih.gov/pubmed/28472712
Casposons are a superfamily of self-synthesizing transposons found in prokaryotes. One identified casposon is homologous to the Cas1 endonuclease and could have evolved into the adaption module of the CRISPR/Cas system and the CRISPR repeats. This opinion publication covers how the casposon system is similar and different from that of CRISPR/Cas and the evidence supporting its evolution into the CRISPR system.