AN ESCHERICHIA-COLI GENE IN SEARCH OF A FUNCTION - PHENOTYPIC EFFECTSOF THE GENE RECENTLY IDENTIFIED AS MURI

Earlier we reported that an open reading frame located at 89.5 min of the Escherichia coli map (ORFI) codes for a protein of unknown functio n that could be overexpressed and purified to homogeneity (G. Baliko, A. Raukas, 1. Boros, and P. Venetianer, Mol. Gen. Genet. 211:326-331, 1988). In the work described here, we attempted to learn the function of this protein by inactivating the chromosomal gene and providing it or its deletion derivatives on temperature-sensitive plasmids. We foun d that the presence of the functional ORFI gene is essential; cells ar e not viable at the nonpermissive temperature or when the region codin g for the C-terminal 50 amino acids of the protein is deleted. At inte rmediate temperatures or when the gene is overexpressed, characteristi c changes occur in cell morphology, nucleoid separation during cell di vision, and supercoiling of plasmids. The possible mechanisms of these effects are discussed in view of the fact that Doublet et al. (P. Dou blet, J. van Heijenoort, and D. Mengin-Lecreulx, J. Bacteriol. 174:577 2-5779, 1992) recently identified the ORFI gene as murI, involved in D -glutamic acid biosynthesis.