Insertion Sequences Revisited

Abstract

This chapter is an update of a survey of insertion sequences (ISs) published in 1998. Researchers have retained the same basic structure: a first section including some key properties of ISs and a second section that defines and describes the different IS families. Throughout the text the authors have tried to compare and contrast the different IS families in terms of their transposition mechanism and control of their transposition activity. Researchers have introduced an additional section concerning bacterial genomes and plasmids since a number of genome sequences have become available over the past three years, and a large number of potential ISs have been identified in several of these. Researchers have also retained a section on eukaryotic insertion sequences. A general pattern for the functional organization of Tpases appears to be emerging from the limited number that have been analyzed. Another general feature of IS elements is that, on insertion, most generate short directly repeated sequences (DR) of the target DNA flanking the IS. Transposition activity is frequently modulated by host factors. The G+C content of family members varies from 70% in the mycobacterial examples to 25% in those isolated from Mycoplasma species. Family members from Mycoplasma species merit special attention.