Shufflon: multi-inversion of four contiguous DNA segments of plasmid R64 creates seven different open reading frames

The IncI alpha plasmid R64 was found to bear a highly mobile DNA segment which was designated as a clustered inversion region (J. Bacteriol. 165, 94-100, 1986). The clustered inversion region consists of four DNA segments designated respectively as A, B, C and D which differ in molecular size and restriction sites. The four DNA segments invert independently or in groups resulting in a complex DNA rearrangement. We now show the nucleotide sequence of the clustered inversion region of R64. The present results suggest that the clustered inversion region is a biological switch to select one of seven open reading frames whose primary structures at the region proximal to N-termini are constant while those at the C-terminal region are variable. A name, "Shufflon" was proposed to call this kind of the clustered inversion region.