Inversions of specific DNA segments in flagellar phase variation of Salmonella and inversion systems of bacteriophages P1 and Mu.

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Abstract
Prophages P1 and Mu produce a trans-acting factor possessing the din+ activity which catalyzes the inversion of the specific DNA segment responsible for flagellar phase variation of Salmonella, din mutants were isolated from P1CMclr100 phage by selecting phages that did not suppress the yh2 mutation of Salmonella in prophage state. No inversion loop structure was detected among DNA forms arising after denaturation and rehybridization of DNA extracted from the din mutants. The DNA fragment containing C region of P1 was cloned on a plasmid vector, pCR1. The resulting hybrid plasmid, pKK2, was shown to possess the din+ activity: the vH2 mutant of Salmonella harboring the plasmid changed the flagellar phase. From analysis of the plasmid by use of BamHI and BglII, the din gene specifying the din+ activity was located near or within the C region of P1. It is highly plausible that the din gene of P1 was also involved in the inversion of the C region. The DNA fragment containing the G and .beta. segments of Mu was cloned on pCR1. The resulting hybrid plasmid, pKK101, also possessed the din+ activity.