Direct repetition of a 1.2 Md DNA sequence is involved in site-specific recombination by the P1 plasmid R68.

R68.45, a mutant R68 plasmid, carries a 1.5 Md DNA insertion near its kanamycin-resistance region. This DNA consists of a 1.2 Md DNA repetition of neighbouring R68-DNA and a 0.3 Md "foreign" DNA fragment that is flanked by this direct DNA repeat. This fragment seems to be involved in the formation of R'68.45 plasmids. Duplication of the 1.2 Md DNA sequence is also involved in site-specific recombination events of RP4. This 1.2 Md DNA fragment has the properties of an IS sequence and is denoted IS8.