Involvement of inorganic polyphosphate in expression of SOS genes

Inorganic polyphosphate (poly(P)) is a linear polymer that has been found i n every organism so far examined. To elucidate the functions of poly(P) in the regulation of gene expression, the level of cellular poly(P) in Escheri chia coli was reduced to a barely detectable concentration by overproductio n of exopolyphosphatase (exopoly(P)ase) with a plasmid encoding yeast exopo ly(P)ase (Shiba et al., Proc. Natl. Acad. Sci. USA 94 (1997) 11210-11215). It was found that exopoly(P)ase-overproducing cells were more sensitive to UV or mitomycin C (MMC) than were control cells. Poly(P) accumulation was o bserved after treatment with MMC, whereas the poly(P) level was below the d etectable level in cells that overproduced exopoly(P)ase. When exopoly(P)as e-overproducing cells were transformed again by a multiple copy number plas mid that carries the polyphosphate kinase gene (ppk), the cells accumulated a great amount of poly(P) and restored the UV and MMC sensitivities to the level of control cells. In exopoly(P)ase-overproducing cells, the expressi on of recA and umuDC were not induced by MMC. In addition, a strain contain ing multiple copies of ppk accumulated not only a large amount of poly(P) b ut also recA mRNA. Since recA expression was induced in a reed-deletion str ain harboring a plasmid with the ppk gene, poly(P) could be necessary for r egulating the expression of SOS genes without depending on the RecA-LexA re gulatory network. (C) 2000 Elsevier Science B.V. All rights reserved.