Mobile DNA

This chapter evaluates two ways by which discrete segments of DNA can move from one region of the genome to another—by transposition, whereby transposable elements can insert in many different sites around the genome; and by conservative site-specific recombination (CSSR), whereby recombination occurs between pairs of specific, related DNA sites to rearrange sequences bound by those specific sites. These recombination systems are widespread and have a profound impact on chromosome structure and function. Virtually all organisms contain transposable elements, and their mobility is a significant contributor to genetic variation. CSSR systems are found mostly in bacteria where they play important roles in bacterial chromosome segregation and in the interactions of viruses and plasmids with their hosts. The chapter begins with an overview of transposition before considering in more detail the mechanisms of action employed by different elements and the strategies used to regulate these processes. It then explores CSSR.