Phase variation in salmonella : analysis of the controlling element of H2 gene expression : gene expression, recombinational control, phase variation, DNA inversion
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In the phase variation system of Salmonella, the alternative expression of Hl and H2 flagella is controlled by a region of DNA adjacent to the H2 structural gene known as the Phase Determinant. The Phase Determinant regulates H2 gene activity via a site specific recombinational event. Electron microscopic evidence and restriction endonuclease site mapping indicate that the recombinational event results in an inversion of a region of DNA 800 bp (base pairs) in length. The inversion process does not depend on the RecA recombinational pathway of E. coli. Plasmids have been constructed in which the expression of non-related genes appear to be under phase variation control. These plasmids have provided evidence concerning the direction of transcription of the H2 structural gene and the position of the H2 promoter.