A Mu gin complementing function and an invertible DNA region in Escherichia coli K-12 are situated on the genetic element e14.

The Gin product catalyzes an inversion of 3,000 base pairs of DNA in the genome of bacteriophage Mu. The orientation of the invertible of G-region determines the host range of the phage. Gin- mutants are complemented by a host function in strain HB101 and several other Escherichia coli K-12 strains. At least three clones in the E. coli gene bank described previously (L. Clarke and J. Carbon, Cell 9:91-99, 1976) contained the gin complementing function. This function, which we named pin, catalyzes an inversion of 1,800 base pairs in the adjacent DNA. The invertible region, named the P-region, together with pin, was further subcloned on pBR322. Conjugation and transduction experiments mapped the pin gene between the genes purB and fabD near position 25 on the E. coli chromosome. Also situated in this region is e14, a cryptic, UV- excisable , genetic element (A. Greener and C.W. Hill, J. Bacteriol . 144:312-321, 1980). We demonstrated that pin and the P-region are part of e 14. The e 14 element was cloned on pBR322 by genetic manipulation techniques in vivo. It has the properties of a defective prophage containing integration and excision functions and a SOS-sensitive repressor.