CRISPR-Cas are adaptive immune systems confer bacteria and archaea with resistance against mobile genetic elements (MGEs). When a prokaryote is exposed to an MGE, adaptation can occur, where a new spacer is incorporated into the CRISPR array. Our understanding of adaptation is beginning to emerge, particularly for the type I-E systems. However, the process of spacer acquisition is still poorly characterised for many other CRISPR-Cas subtypes. The talk will discuss adaptation in the type I-F CRISPR-Cas system of Pectobacterium atrosepticum. Type I-F systems are characterised by a unique fusion of the adaptation protein Cas2 with Cas3, the protein that is also responsible for target destruction during interference. In addition, the Cas2-3 fusion protein forms an adaptation complex with Cas1. Our recent characterisation of the adaptation mechanism of the type I-F system will be presented, which involves using newly developed in vitro assays, in combination with in vivo next generation sequencing experiments.