IS4 at its chromosomal site in E. coli K12

Summary IS4 DNA has been isolated in pure form. Hybridization of this DNA against restricted DNA of several E.coli K12 strains by Southern's blotting technique has shown that, in most strains, only one copy of IS4 is present. Though the restriction fragments around this site differ in size, IS4 can be shown always to be located at the same site. In one strain, one additional copy has been found in a new location. In this strain, IS4 in its original location has been retained.